Limited joint mobility (LJM), beginning typically in the fifth finger and moving radially, affecting interphalangeal, metacarpal-phalangeal, and large joints, is the earliest clinically apparent complication of diabetes in childhood and adolescence. It is painless and not disabling. Approximately 50% of post-adolescent patients with more than 5 years duration of diabetes are affected, with age being more important than duration of diabetes, as is the case with other complications. Growth failure is more frequent in the presence of LJM, although correlations with diabetic control have not been found. Variations in frequency in various reports, including high prevalence in controls or relatives, appear to be related to the quality of the examination; simple inspection with hands pressed flat on the table top or together in the prayer position is inadequate; passive extension must be performed. Although differential diagnosis from other conditions causing limitation of the fingers in diabetes would appear simple, LJM has been confused with other conditions which can be distinguished by the presence of pain or paresthesias, neurologic findings, disability, finger-locking, swelling, muscle atrophy, palmar skin or fascial thickening, absence of typical distribution, calcification of the vessels and, particularly, the age group affected. That the periarticular thickening found on examination and demonstrated on roentgenograms reflects generalized abnormalities is suggested by association with thick tight waxy skin, decreased pulmonary function, and association with retinopathy, nephropathy, and neuropathy, independently of duration of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)