Hyla cinerea and H. gratiosa are closely related treefrogs that differ at metamorphosis in the length of the hind limb relative to snout vent length. A developmental series of larvae of the two species raised under uniform laboratory conditions reveals that H. cinerea have proportionately longer legs at metamorphosis than H. gratiosa for the following reasons: 1) Hyla cinerea initiate limb growth at a smaller body size than H. gratiosa, 2) H. cinerea have a faster rate of limb growth, and 3) body growth rates in H. cinerea and H. gratiosa are nearly identical until just before metamorphosis.