Stranger things have happened, but it was practically surreal to witness Roky Erickson’s debut on a New York stage Friday night, when the Texas garage-rock legend headlined a sold-out concert at Brooklyn’s Southpaw.

Sidelined for much of the past 40 years with varying degrees of mental illness, Mr. Erickson had become one of the ghosts he loves to sing about. At home in his native Austin, Texas, he was a character out of a rock ‘n’ roll gothic, still possessed of weird songwriting genius but not doing too much about it. In a city notorious for its local eccentrics and bohemian tolerance, the performer was at once a cautionary figure — the ultimate psychedelic casualty — and an iconic cult hero, the man whom a legion of demons could not diminish. His current comeback could not have been consciously timed: The singer’s mental stability only began to improve after his youngest brother Sumner became his legal guardian in 2001. He finally returned to the stage in late 2005.

It was a vigorous and healthy singer who plugged in at Southpaw. Mr. Erickson, who turns 60 this summer, looked shockingly fit, and had lost little of his mojo. When he launched into “You’re Gonna Miss Me,” his 1966 breakthrough hit with the Austin psych-rock progenitors the 13th Floor Elevators, the unearthly howl that kick-starts the song was as hair-raising as ever. Backed by his three-piece band the Explosives, the singer appeared delighted just to meet the surging crowd with his eyes, strumming away in what looked like a bowling shirt.

“Roky Erickson to this day is one of the out-and-out wildest rock singers,” ZZ Top’s Billy Gibbons testifies in a new documentary about Mr. Erickson, “You’re Gonna Miss Me,” which Palm Pictures will release on DVD in July. “The talent behind Roky’s voice is the mystery factor that no one could touch. To this day, he stands alone and is revered as such an unusual artist, because he had the gift of that wonderful voice, which is just crazy.”

Mr. Erickson also was blessed (and cursed) with a hyperactive imagination that was, perhaps, made even more vivid through his use of psychedelic drugs in the 1960s. When he pleaded insanity to escape a jail term for possession of a marijuana joint in 1969, his lawyer’s bad advice landed him in the Rusk State Hospital for the Criminally Insane, where electroconvulsive therapy and Thorazine treatments guaranteed he would never be the same.

Amazingly, the singer returned to bold form by the mid-1970s, fronting his band the Aliens and recording songs that obsessed over demonic forces, drive-in movie horror imagery, and weird science. He was perfectly in tune with the budding punk era — could there be a more ideal outcast? — and put a hallucinatory spell over a new generation of rock fans who might have laughed when Mr. Erickson had himself legally declared an extraterrestrial, but got spooked when they heard the supernatural cackle in his throat.

The hour-plus set at Southpaw drew deeply on that era, as Mr. Erickson cranked through such bug-eyed anthems as “Creature With the Atom Brain” and “Don’t Shake Me, Lucifer,” straightforward rave-ups that invited the audience to listen past the choogle and hear the singer elucidate his nightmares.

Of course, the music is and was therapeutic. “Two-Headed Dog (Red Temple Prayer)” was penned after he was declared legally sane in 1972 and released from the mental institution, and its twisted visions of biological experiments in the Kremlin may sound like comicbook fodder, but they were Mr. Erickson’s daily reality. What was most rewarding about the show was Mr. Erickson’s evident glee in being onstage, and the zest that infected his stomping, three-chord rock. There’s just something about being a room with several hundred beer-soaked adults, pumping a fist and shouting “Two-headed dog! Two-headed dog!” in unison, that feels inspiring.

Paranoia is not everything, of course. For Mr. Erickson, for a tragically long time, it was the only thing. But as he proved this weekend, even demons can take a holiday. Will he miss them like we missed him? There’s no telling, but for now, at least, one of rock ‘n’ roll’s darkest sagas looks to have a happy ending.