Apollo 17 Commander Eugene Cernan's departing footprints are still the last to mark the lunar surface, and the camera he says he should have photographed them with also remains there.
"I left my Hasselblad camera there with the lens pointing up at the zenith, the idea being someday someone would come back and find out how much deterioration solar cosmic radiation had on the glass," he said.
Cernan made the remarks ahead of Friday's 40th anniversary of the Apollo 17 launch, The Daily Telegraph reported.
"So, going up the ladder, I never took a photo of my last footstep. How dumb! Wouldn't it have been better to take the camera with me, get the shot, take the film pack off and then (for weight restrictions) throw the camera away?"
Cernan, now 78, said he believed in 1972 his mission "wasn't the end but the beginning" for manned exploration of the moon, and had believed an astronaut would have set foot on Mars by the end of the 20th century.
Mars is being held up as a desirable destination for future manned space missions but Cernan said a return to the moon should be a first step on that journey.
"I do think we need to go to the moon first to set up a base so we can use more advanced propulsion techniques," he said.