Objective To determine the factors associated with poor glycemic control in children (1‐10 years), adolescents (11‐18 years) and young adults (19‐40 years) with Type 1 Diabetes Mellitus (T1DM) in Kilimanjaro Christian Medical Center (KCMC) in Moshi, Mount Meru Regional Referral Hospital (MMRRH) and Meru District Hospital (MDH) in Arusha, Tanzania. Methods Cross sectional study of 150 participants conducted from January to June 2019, data was collected by structured questionnaire and analyzed using SPSS version 23. Results The mean HbA1c was 12.3 ± 2.2%, 146 had poor glycemic control (HbA1c > 7.5%). BMI, insulin regime and caretaker education were associated with poor glycemic control. There were 16 participants diagnosed in DKA and the most frequently reported complications in the prior 3 months were hyperglycemia (n = 25), DKA (n = 18) and hypoglycemia (n = 4). Conclusions Glycemic control is still very poor particularly in adolescents. Significant associations with glycemic control were higher BMI, insulin regime and guardian education. The study revealed lower prevalence of DKA at diagnosis compared to previous studies.