Nicholas Nixon is a family man. Mr. Nixon (b. 1947) was an only child who married into a large family and determined to record its intricate and changing relationships. Every year there is an addition to his series of photographs of his wife and her three sisters, the Brown sisters, that now includes, in the book by that name just released by the Museum of Modern Art, 33 pictures. His determination to document his family extended to photographing his father-in-law when Mr. Brown became terminally ill, and that experience got him interested in the possibilities of portraits of people in hospital settings. “Patients,” the exhibition of Mr. Nixon’s work currently at the Yossi Milo Gallery, consists of 18 black-and-white, 24-by-20-inch pictures of seriously ill people, all except one of which were taken in the last three years in four Boston-area hospitals.

The six tightly framed portraits one sees along the west wall make a dramatic impact upon entering the gallery. The heads that fill each frame are somewhat monumental, and somewhat abstract in their simplicity. Mr. Nixon shoots with an 8-by-10-inch view camera and ordinarily produces contact prints of his negatives, but for this series he has enlarged them; there is little loss of detail and a considerable gain in effect in this medium-sized format. The first of the six is “Maureen Chimiello, Boston Medical Center” (2007), the subject of which was hospitalized after a household accident burned her on the throat. Her neck is swaddled in bandages. Above the gauze is a sturdy face framed in straight white hair. Her eyes look to the lower left, to an aged male hand that rests gently on her shoulder, all we see of her comforter.

“Edwin Short, Boston” (2007) shows a 101-year-old man in the geriatric unit. Mr. Nixon shot this portrait very close up, so we only see Mr. Short’s face from the forehead down, and from the left cheek across. The camera is close enough so that the white stubble of Mr. Short’s beard stands out delicately against his black skin. But his gnarled mouth is what most draws attention; is it twisted in pain or determination? His eyes, which have seen a lot, stare at the camera.

The next picture shows us not the face, but the back of the shaved head of “John Royston, Easton, Mass.” (2006). A ridge-like scar is visible above his right ear, and there is another scar just in front of it. Except for the ear, the solid shaved head would be an abstract form, similar to one of Constantin Brâncusi’s sculptures. Royston had a brain tumor, which was operated on three times. The ridge in his head is a tube for fluid drainage. There is another portrait of him further along the wall where we see his face in profile. Apparently a strong man, he has a face that is gentle, resigned. Since the picture was taken, he has died.

There are several pictures of children. “Alexla Laci, Boston” (2007) shows a miniature baby with wrinkled skin and a tube attached to her nose who too easily fits in the arm of the white-gowned doctor or nurse who is holding her. She was born at 26 weeks to a drug-addicted homeless woman, and later placed in foster care. “Elizabeth and Andrew Kan, Lexington, Mass.” (2007) shows adorable infant twins in gowns covered with printed flowers. Elizabeth has a plastic tube attached to her nose, and later died of blood cancer. Andrew has a shocked expression, despite the fact that he cannot possibly comprehend his circumstances. “Serenity Fountaner, Boston” (2006) shows a child who was 3 months old when Mr. Nixon took his picture of her. He shot her lying on her back in profile with an extremely slow exposure speed, so that the blurred movement of her hands animates the picture. A few moments later, she underwent a successful heart surgery.

There is nothing morbid about these images, not even the portrait of “Suzanne Richardson, Boston” (2005), taken 10 minutes before she died of gastric cancer. Richardson, a former dean of Harvard Law School, has been wasted by her disease. Her head lies on a pillow with her eyes shut, and various plastic tubes in place, but she has her dignity intact.

Richardson consented to have Mr. Nixon take her picture, as did all his other “patients” or their guardians. He was not a casual interloper in the hospitals he photographed in, but got to know his subjects and gain their confidence. They wanted records of their ordeals, for themselves if they survived, for their loved ones if they did not.

Richard Avedon famously photographed his father Jacob’s terminal decline. W. Eugene Smith’s picture of the deformed Tomoko Uemura, a victim of mercury pollution, is a classic image. Peter Hujar shot his friend Sidney Faulkner dying of cancer. Sickness is a genre. Mr. Nixon’s oeuvre has mostly been concerned with the quotidian dramas of life: not just the inevitable aging of the Brown sisters over a third of a century, but the minutiae of his own children’s infancies and development, and the affectionate intimacy of couples. Illness, even death, is part of a continuum to which he is a witness, not a voyeur.

Until February 16 (525 W. 25th St., between Tenth and Eleventh avenues, 212-414-0370).