The validity of otolith ageing in Puerto Rico was examined using known-age largemouth bass (Micropterus salmoides) in Lucchetti Reservoir. Age-0 largemouth bass were tagged with binary-coded wire microtags and stocked into the reservoir on 6 separate events between April 1992 and May 1996. Fish were collected throughout the study at ages 1-3 and otoliths and microtags were removed from tagged bass. Of 36 age-1 and older tagged bass recovered, 50% had no discernible otolith rings (read as age 0). Observed ages of all otoliths agreed with true ages only 14% of the time, and often differed by 2 years. Thus, we concluded that observed opaque bands were not annuli and this ageing technique is invalid for tropical largemouth bass. Length-at-age keys and length-frequency distributions were developed as alternative techniques for age determination, and these methods proved effective for Lucchetti Reservoir.