Growth patterns that lead to sexual dimorphism in adults are not well quantified. We measured 49 skeletal dimensions in male and female Chinchilla lanigera from radiographs of growing individuals taken during 320 days. Measurements for each individual were fit with a nonlinear Gompertz equation to quantify growth patterns. Differences in Gompertz parameters between sexes were compared with a t-test. Most significant differences between sexes in growth and final size were in the pelvic girdle (which formed the birth canal) and viscerocranium. Sexual dimorphism in the viscerocranium may support the hypothesis that differences in use of ecological niche often causes sexual dimorphism where females are larger than males.