Radio-telemetry was used to study spatial ecology of a Cottonmouth (Agkistrodon piscivorus) population in eastern Texas. I examined effects of sex, reproductive state, and body size on spatial use within a riparian habitat. Snakes inhabited a relatively linear environment, restricting movements to the vicinity of the stream. Males occupied larger home ranges than both gravid and nongravid females. Gravid females exhibited marginally larger home ranges than nongravid females, but any effects attributable to reproductive state were relatively small when compared to sex differences in spatial use. Body size was positively correlated with home-range size but did not account for observed home-range differences among population subunits.