Abstract Objectives This study aimed to determine the effects of continuous subcutaneous insulin infusion (CSII) treatment on anthropometric measurements, mean HbA1c, and insulin dosage in patients diagnosed under 5 years of age and compare with multiple-dose injection therapy (MDI). Methods Children with type 1 diabetes mellitus, diagnosed <5 years since 2000 and their 19-year follow-up were evaluated retrospectively. Weight, height, body mass index (BMI), blood pressure, and HbA1c values were recorded for each visit. Results Hundred and five patients (58.1% female, 41.9% male) were included in the study. Sixty-three (60 %) patients were treated by CSII and 42 (40%) by MDI. Mean age at diagnosis was 2.68 ± 1.42 and 3.29 ± 1.30 years respectively. Mean follow-up was 7.42 ± 4.76 and 6.01 ± 4.41 years respectively. For each group, weight standard deviation score (SDS) increased significantly in the first year after the diagnosis (p<0.001), and with the onset of puberty weight SDS decreased significantly (p<0.001). The trend of weight and BMI SDS changes over the years showed similar characteristics in both groups. During follow-up height SDS was similar in both groups except in Tanner stage 5. When puberty was completed, mean height SDS was 0.51 ± 1.03 in CSII and −0.31 ± 0.75 in the MDI group (p: 0.029). Mean HbA1c was significantly lower in the CSII group (7.62 ± 0.82 and 8.17 ± 1.22 respectively). Systolic and diastolic blood pressure change trends during the follow-up were also similar in both groups. Conclusions CSII treatment had positive effects on metabolic control and height SDS in patients with early-onset diabetes without increasing BMI.