Striped bass (Morone saxatilis) were sampled during summer and winter in the St. Johns River, Florida, to determine effects of summertime thermal stress on fish condition. Regressions of log weight on log length for winter and summer fish had significantly different slopes (P < 0.001) indicating larger fish were less robust than smaller fish in summer as compared to winter. Data were arbitrarily separated into 3 size categories (small = <331 mm TL; medium = 331-500 mm TL; large = >500 mm TL) to investigate thermal related stress by size. No negative seasonal impacts could be detected for the small fish category. Although the seasonal slopes were not significantly different for either the medium or large fish categories, significant differences (P < 0.001) in line elevations indicated that summer fish weighed less for any given length than winter fish. Analysis of back-transformed, adjusted, mean log weights generated during analysis of covariance indicated, a 2.3%, 16.3%, and 22.0% difference between winter and summer weights for small, medium, and large fish, respectively.