Banana-Sam was found wandering Stern Grove Park about three miles from the zoo by a passerby Saturday afternoon.
Authorities say passerby was able to coax the monkey into his backpack. The passerby then called San Francisco police, who recovered the monkey and returned Banana-Sam to the San Francisco Zoo.
Zoo officials say Banana-Sam was thoroughly checked out upon his return and the monkey is healthy, although the zoo says he was hungry, thirsty and trembling.
Banana-Sam was thought to have been stolen from the zoo; it's unclear if this is still the case. Zoo officials had been worried about Banana-Sam due to his old age and his special nutritional needs, and had offered a sizable reward for his safe return.
It is illegal to own a monkey as a pet in California.