Data on musculoskeletal problems were collected among samples of letter carriers who were subject to a recent weight increase and those who were not. In addition, comparable data were collected for two groups of controls: gas meter readers who walk on the job, but do not bear a load as do letter carriers, and postal clerks who neither walk nor carry a load. Letter carriers experience excess shoulder, and perhaps neck and back, disability due to their weight bearing on the job. Increase in weight carried is also related to excess shoulder disability among letter carriers. These differences persist after controlling for age, number of years on the job, quetelete ratio and previous work that involved lifting or carrying.