This study aimed to document demographic parameters of an Andean dart frog, Andinobates opisthomelas. We used a photoidentification method to recognize recaptured individuals during a six month study of a population on a small island in a reservoir in the Cordillera Central of Colombia. Reproductively active males were identified based upon the presence of vocal sacs or observed calling or parental care behaviors (carrying from one to three tadpoles on their backs). Minimum size at first reproduction for males was estimated at 12.9 mm snout-vent length. Only 4% of captured individuals were smaller than this size; the remaining individuals were classified as either reproductively active males or other adults. The survival rates and detectabilities of these two groups were compared in both wet and dry season periods using maximum likelihood model fitting methods. Survival rates did not differ between groups but was related to body size, with smaller adult individuals having lower survival rates. Reproductively active males had higher detectabilities than other adult individuals, and both classes exhibited higher detectabilities in larger individuals and in the dry season sampling periods. Herpetologists are encouraged to use methods that permit decomposition of encounter rates into their component parameters (survival rate and detection probability) to facilitate identification of factors influencing population dynamics and permit meaningful comparisons among studies.