Spring spawning migrations of paddlefish Polyodon spathula into the River Missouri above Fort Peck Reservoir, Montana were investigated with radio-telemetry during 2006-2009. Selected migration characteristics (total movement, rate of movement, maximum upriver ascent, duration of the migration, upriver residence time and spawning periodicity) were compared between sexes and among years. Paddlefish exhibited sexual dimorphisms in selected measures of migratory behavior. Females typically moved at a faster rate (mean, 13.4 km/ day for females versus 10.1 km/day for males) and remained in the river a shorter time (mean, 40 days) than did males (mean, 45 days). Females and males exhibited similar total movements, upriver residence times and mean maximum ascents. Spawning periodicity was shorter for males (mean, 1.5 years) than females (mean, 2.3 years). Total movement, movement rate, mean duration of the spawning migration and upriver residence time of both sexes differed among years. Results from this study indicate that certain analyses of paddlefish migrations and migratory behavior should be undertaken separately for female and male fish.