The incidence of type 1 diabetes in children from Aragon (a population of the North of Spain) is reported determining the relations between the onset of type 1 diabetes and gender, age at diagnosis, genetic risk (HLA class II genes) or climatology factors. The population at risk was all 0-14 year-old inhabitants. Patients were identified from five sources: hospitals, primary assistance, endocrinologists, diabetic associations and diabetes camps. The degree of ascertainment was 98.93%. HLA genetic study was performed. Annual incidence was 16.4 per 100,000 per year (95% CI: 14.7-18.2). This incidence was significantly higher in males than in females, 18.7 versus 14.2 (p<0.02), and increased with age. The haplotypes (DR3)-DQB1*0201/(DR4)-DQB1*0302 and (DR3)-DQB1*0201/(DR7)-DQB1*0202 conferred the highest risk of type 1 diabetes. A relative high incidence of type 1 diabetes mellitus has been demonstrated in the Northeast of Spain, and it does not support south-to-north incidence gradient in Europe. Haplotypes that conferred a higher risk of disease agree with those founded in other Caucasic populations.