The aim of this report was to evaluate the incidence of Type 1 diabetes mellitus (T1DM) in the district of Catania (eastern Sicily) in children under 15 yr of age over a ten-yr period (01/01/1989 - 31/12/1998) in relation to age, sex, monthly-seasonal variability, calendar yr and spatial clustering. The estimated completeness of our register was 99.2%. The overall incidence rate was 12.38 per 100,000 during the period of the study. Twenty-four percent of cases were 0-4 yr at diagnosis, 42% were 5-9 yr and 34% were 10-14 yr. More males (no. 148) than females (no. 125) were newly diagnosed with a male/female ratio similar to the base population ratio in the range 0-14 yr and within age groups. The study revealed a non-random spatial distribution of T1DM incidence in children not accounted for by known demographic factors. A significant seasonal pattern and temporal trend of incidence were also detected.