To determine the factors at diagnosis predictive of changes in residual beta-cell function and metabolic control in Type 1 diabetes, 125 patients older than 7 years of age consecutively diagnosed between March 1986 and June 1991 were followed prospectively for two years. The effect of age, gender and the presence of ketoacidosis (DKA) and islet-cell antibodies (ICA) on beta-cell function, metabolic control and insulin requirements were studied by multivariate analysis of variance (repeated measurements over time) in 90 patients who completed follow-up. DKA had an independent negative effect on residual beta-cell function over time (p = 0.001). ICA-positive patients had lower residual beta-cell function at the end of follow-up (p < 0.05), but overall differences were not significant. DKA and younger age had an independent negative influence on metabolic control (p < 0.05) and insulin requirements (p < 0.001) over time. It is concluded that residual beta-cell function in Type 1 diabetic patients two years after diagnosis was independently influenced by DKA and ICA at diagnosis. Moreover, DKA and age influenced metabolic control and could thus be used to predict those patients with rapidly deteriorating metabolic control who might benefit from a more intensive therapeutic approach.