It has been hypothesized than morphological diversity within clades can be generated by simple alterations of shared developmental programs. However, few studies have examined changes in heterochrony, the rate and timing of developmental events, in an explicitly phylogenetic context. We studied how developmental patterns have changed phylogenetically in the northern swordtail clade of Xiphophorus. We reared individuals of an outgroup and seven of nine species in the clade and followed their development for ~300 days. For each individual, we used nonlinear regression to estimate three growth parameters: growth rate, adult body size, and age of cessation of growth. We estimated sword growth rates in males by linear regression. We then used the means of these growth parameters to construct standard growth curves for each species and to study growth patterns in a phylogenetic context. A combined phylogeny was constructed from both phenotypic and DNA sequence data. The phenotypic data set, compiled from the literature, consisted of 86 morphological, pigmentation, behavioral, and random amplified polymorphic DNA characters, many of which had not been used before for phylogenetic analysis. DNA sequence data from three genes for a total of 1284 bases were also obtained from the literature and included in the analysis. Relationships between growth parameters were examined by phylogenetically independent contrasts in relation to seven different phylogenies based on the most-parsimonious trees generated from the phenotypic, DNA sequence, and combined data sets; this allowed us to identify relationships between variables that were not sensitive to ambiguities in Xiphophorus phylogeny. Our analysis revealed statistically significant correlations between female body size and male body size, and between female growth rate and male sword growth rate, for all seven phylogenies. Marginally statistically significant relationships were also identified between female body size and female growth rate, and between female growth rate and male body size. We relate these relationships to what is known about the ecology, genetics, and behavior of Xiphophorus to better understand the evolution of growth patterns of both the body as a whole and the sword in particular. The relationship of these data to the evolution of swords is discussed.