We estimated the median and maximum life spans of 1,459 spiny rats (Proechimys semispinosus) from mark–recapture data collected monthly from 4 island populations in central Panama over a 9-year period. We plotted frequency distributions of life spans of males and females over 5-month age intervals, proportions of males and females surviving versus age, and survivorship curves for males and females. Median life spans ranged from 6.5 to 10 months, and maximum life spans ranged from 36 to 53 months. Frequency distributions were skewed to the right, showing a greater frequency of individuals with shorter life spans. Life spans did not differ between sexes or among islands. Survival curves were linear for both males and females within 1 population and convex for both sexes within the other 3 populations. We thereby provided the 1st quantitative analysis of life spans and survival curves for any small tropical rodent.