Cambarus elkensis (Elk River crayfish) was seined and dip-netted monthly during June through August and October through November 2003, and March through May 2004 from Left Fork Holly River in the Elk River drainage, West Virginia, U.S.A. Crayfish reproductive form was classified, and then individuals measured and returned to the stream. Carapace-length (CL) frequency analysis identified five overlapping year classes with growth progressing over a 5-year life span. Ovigerous females were collected in summer (June) and an individual with attached young in October, but young-of-the-year (Y-O-Y) crayfish did not appear in the collections until late winter (March). Juveniles and Y-O-Y dominated the collections and grew rapidly, reaching sexual maturity (≥ 29 mm CL) in 30-36 months. Growth continued but slowed in the older mature crayfish with the largest individuals (> 50 mm CL) disappearing from the collections sometime between fall and spring in the fifth year of life. Fastest growing individuals could have reproduced three times during their life. The overall sex ratio of 1265 crayfish favored females 0.87∶1. Females identified as form I individuals based on annulus ventralis architecture and presence of glair gland and ova had significantly wider pleons, longer chelae, and heavier bodies than similar CL form II female crayfish lacking these features. Form I males also weighed significantly more and had longer chelae than form II males of similar CL. This is the first evidence of the existence of reproductive form alternation in females in the genus Cambarus.