The purpose of this study was to investigate the effect of diet and L-carnitine supplementation on lipoma size and bodyweight in adult budgerigars (Melopsittacus undulatus). Seventeen budgerigars with naturally occurring cervical lipomas and 15 without lipomas were assigned to groups (4–6 birds/group) and fed 1 of 3 diets for a period of 102 days. The diets fed were a 100% seed mixture, a commercially produced low-fat pelleted diet, and the same pelleted diet supplemented with approximately 1000 mg/kg L-carnitine. Birds receiving pellets were also offered a small amount of seed to improve acceptance. Bodyweight and lipoma size were recorded for each bird at 2- to 4-week intervals. Bodyweight increased in all budgerigars (with and without lipomas) receiving 100%-seed diets. Of these birds, 83% gained >10% of their initial bodyweight. Lipoma size decreased in budgerigars that were fed the pelleted diet supplemented with L-carnitine. These data suggest that feeding a 100%-seed diet may result in inappropriate weight gain in budgerigars and that the use of L-carnitine supplementation in the management of lipomas deserves further investigation.