The treefrog Hypsiboas bischoffi is endemic to southern and southeastern Brazil occurring in submontane and montane areas of the Brazilian Atlantic Forest. Here, we focus on geographic variation in morphological traits of H. bischoffi by analyzing the distribution of two distinct color pattern forms (striped and nonstriped) to examine the hypothesis that color pattern is polymorphic within populations throughout its range. We additionally describe variation in several morphometric traits and examine their association with either color pattern or environmental gradients across the range. Our results show that the two color pattern forms are parapatric, with the striped and nonstriped forms occurring in the northern and southern parts of the species range, respectively. The two forms were not observed to co-occur, but nonstriped individuals appeared to present somewhat intermediate color patterns near the putative contact zone between the two forms. Multivariate analysis of morphometric variation showed that variation in body size explains most of the observed variation, but neither body size nor further morphometric variation was associated with color pattern or geographic distance between populations. Body size appeared instead to be associated with local levels of summer precipitation. The geographic differentiation pattern in H. bischoffi is apparently concordant with those observed for a few other codistributed organisms in the Brazilian Atlantic Forest.