An easy and reproducible technique was sought to determine the relative stage of skeletal maturity of small cetaceans. Flippers from 146 Dall's porpoises, Phocoenoides dalli, and 100 Pilot whales, Globicephala macrorhyncha, were radio-graphed for the study. Six stages of development were outlined with one stage possibly being an indicator of sexual maturity. This technique may also be employed, once a large enough sample size has been collected, for large cetaceans, including baleen whales.