In sharp-tailed grouse (Pedioecetes phasianellus) and prairie chickens (Tympanuchus cupido) the pattern of crown feathers varied according to sex. Crown feathers of males are dark with a buff-colored edging; crown feathers of females have alternating buff-colored and dark cross-bars. Thirty observers averaged 93.0% in accuracy in 10,879 attempts to sex sharptails by means of crown feathers. On tail feathers accuracy averaged 87.0% among 26 observers in 4191 tries. On prairie chickens 22 observers averaged 85.3% on crown feathers; on tail feathers they averaged 90.7%. One person was 98.2% accurate on sharptail crown feathers; another was 98.5% accurate on prairie chicken crown feathers. The use of sharptail crown feathers gave a larger sample and more nearly accurate sexing than the use of tail feathers. Pigmentation of the brow was intermediate in accuracy as sex criterion in both species. Accuracy of crown and tail methods was improved when whole birds were examined rather than mounted feather specimens. High accuracy resulted at checking stations when agreement in any 2 of the 3 external characters (crown, brow, and tail) was used. All tests were made using materials from internally sexed birds. Patterns of crown feathers are useful for sexing grouse in field studies.