The study aimedto evaluate the cognitive functioning of children and adolescents with type 1 diabetes mellitus (T1DM) recruited from the IAHULA Endocrinology Outpatient Unit and to compare it to that of non-diabetics as to investigate the influence on cognition of factors re-lated to the disease. An analytical, cross-sectional observational study was carried out on a group of 30 patients with T1DM between 8 and 16 years of age and on a control group of 30 individuals matched by age, gender, education, and socioeconomic status. Interrogation and review of medi-cal records to obtain data on the clinical characteristics and treatment of T1DM were conducted. The WISC IV test was then applied to evaluate cognition and intellectual coefficient (IQ). The average age of the diabetic patients was 13.27±2.31 years, and half of them were male. Lower scores were found in the different domains of the WISC IV in the group with T1DM (p<0.01). The IQ was found to be lower in children with T1DM than in con-trols (75.47±13.87 vs. 88.57±11.06; p=0.0001). Likewise, a higher fre-quency of IQ scores below the 10th percentile was observed in the diabetic children (63.3% vs. 33.3%; p=0.02; Odds ratio: 3.45; 95%CI: 1.19-9.99). It was concluded that T1DM negatively impacts the cognitive performance of children and adolescents. Cognitive evaluation of these patients is recom-mended, as it could affect their daily life.