Several histological studies have attempted to derive life history parameters of sauropod dinosaurs. However, verification of sexual maturity and growth rate has been impeded by strong remodeling in sampled sauropod long bones. Here, for the first time, histological variation in the rib cage of Camarasaurus sp. is studied based on a single, relatively small, mature individual. The focus is on the growth history of this individual and its implications for sauropod growth, age, and sexual maturity. Different bone tissue types were observed in different skeletal elements. The long bones show nearly completely remodeled fibrolamellar bone, whereas the ribs show primary zonal bone, with fewer secondary osteons. Histology reveals that the general direction of growth in the rib shaft was from proximal to distal. Therefore, the proximal end of the rib shaft, where growth originated, was determined to be the best sampling area in ribs, providing an almost complete growth record. This study provides the most complete growth record for a sauropod so far, and indicates that it took 40 years for Camarasaurus sp. to reach full size and 18–19 years to become sexually mature. These results show that the growth rate and the point of sexual maturity for a small sauropod are intermediate between the widely divergent previous estimates. With a larger database of rib samples from more individuals of different ontogenetic stages, this approach could yield growth curves for other sauropod taxa.