A study on the biology of the sorghum midge, Contarinia sorghicola Coq., and the damage and crop loss it causes was carried out under field conditions during the main planting season at Mbita, in Western Kenya. The developmental period from egg to adult ranged from 17 to 34 days with a mean of 23 days. On average, 3.2 adult midges emerged from each damaged spikelet. Adult emergence was bimodal, with a major morning peak and minor late afternoon peak. A predator, Diaperasticus erythrocephala Olivier (Dermaptera: Forficulidae), was found preying on newly emerged adults. The level of damage varied among 38 sorghum lines tested, with the size of the panicle (r = 0.73; P < 0.05) and the number of days to 50% flowering (r = 0.49; P < 0.001) influencing the level. The level of damage for the sorghum variety Serena ranged from 1.8 to 97.7% and grain yield from 22.3 to 0.9 kg/50 m2, respectively for plantings during the months of March–June. The relationship between damage and crop loss was almost perfect (r = 0.998; P < 0.001).