Age-based analysis of the stoplight parrotfish Sparisoma viride was used to examine whether observed differences in their abundance and size structure among reefs in a cross-shelf portion of the upper Florida Keys could be explained by variation in demographic rates. Annual and daily sagittal otolith increments were enumerated for 176 individuals collected from replicates of reefs in two strata, inshore and offshore reefs (2–6 m depth). von Bertalanffy growth functions fitted to size-at-age plots for each site were similar between reefs within each stratum (inshore and offshore), but differed between strata. Sparisoma viride on offshore reefs attained greater average standard length (LS) at age, greater mean asymptotic size and were longer lived than fish from inshore reefs. Fish on inshore reefs attained only half the maximum age observed on offshore reefs (4 v. 8 years, respectively). No terminal phase fish >4 years of age were found on either reef type. Estimates of mortality rates from age-frequency data of collected fish revealed higher mortality on inshore reefs. Demographic variables obtained in this study were similar to published values for S. viride from Caribbean reefs but differed significantly from published values from reefs at a similar latitude (Bahamas), reflecting high demographic plasticity on both local and regional scales.