Abstract A population of pheasants was studied for 4 years in southern Sweden to determine how sexual selection operates among males. Morphological characters, viability, dominance, territory quality, date of territorial establishment, harem size and reproductive success of males were measured; 81 males and 101 females were radio-tracked. The spur length of males was the most important predictor of harem size. Phenotypic condition and viability were significantly related to spur length, the best single predictor of the reproductive success of males. These are the first data to show that a sexually selected male character correlates significantly with male viability. The results support models suggesting that viability-based processes can contribute to the evolution of mate choice and secondary sexual characters.