A better understanding of the remission phase, while residual beta-cell function is still present in recently diagnosed type 1 (insulin dependent) diabetes mellitus (IDDM), is very important because of the potential for pharmacological intervention to preserve this function. To evaluate the natural course and characteristics of the remission phase in children and adolescents with IDDM, a retrospective study was performed on patients diagnosed with IDDM under the age of 18 years during the years 1991-1998. Sixty-two patients whose medical records were available were included in the study. Data were collected by reviewing the hospital records of patients from the time of diagnosis through the first 24 months after diagnosis. The duration of symptoms and history of infection prior to presentation, diabetic ketoacidosis (DKA) at diagnosis, length of hospitalization, initial glucose level, basal C-peptide levels at diagnosis, daily insulin requirements per kg body weight and HbA1c at diagnosis and at each visit were recorded. Thirty-five patients (56.5%) entered partial remission. We observed similar remission rates in those aged <10 and > or =10 years at diagnosis and in boys and girls. History of infection and presentation with DKA were associated with a lower rate of remission (p<0.001, p<0.0001, respectively) and were more commonly observed under the age of 10 years (p<0.0001, p<0.0001, respectively). The average insulin requirements per kg body weight calculated at diagnosis decreased with increasing age (r = -0.31, p = 0.012). The length of time until remission was 1.36+/-1.03 (mean +/- SD) months and positively correlated with insulin requirements at discharge from the hospital (r = 0.63, p<0.0001). Mean duration of remission was 11.67+/-5.82 months and was much longer in boys than girls (p<0.05). Six patients, all boys, entered total remission for 3.80+/-3.73 months. HbA1c concentrations in the first year of the disease were significantly lower in patients who underwent a remission phase (7.31+/-1.24% vs. 8.24+/-1.47%, p <0.05). However, this difference was not observed during the second year of the disease. In conclusion, history of infection prior to presentation and DKA at diagnosis were associated with young age and were the most important factors negatively influencing the remission rate in newly diagnosed IDDM patients.