Dissertation (MMED Pediatric and Child Health)Patients with diabetes mellitus present with acute and long term complications with different severity which otherwise if not treated may lead to permanent organ damage renal failure, blindness, heart and cerebrovascular diseases or death. It’s paramount to achieve the best optimal blood glucose sustained at near-normal through proper monitoring of food, exercise, insulin and regular clinic attendance for glucose monitoring. This study was conducted in attempt to determine the factors associated with poor glycemic control and the common acute complications among children and adolescents with type 1 diabetes mellitus aged 1 to 19 years attending clinics at Dodoma and Iringa regional referral hospitals. The cross-sectional hospital based study was conducted, where 125 patients with diabetes mellitus aged 1 to 19 years attending at diabetic clinics enrolled. A fully clinical history was taken, demographics, and physical examinations done on each patient and all information recorded. Investigations including the C-Peptide, HbA1c, blood glucose and urine for ketone were done. Patients who had high HbA1c above the recommended value (>7.5%) by American Diabetes Association were considered to have poor glycemic control and factors associated with glycemic control were determined. Out of 125 enrolled patients, 66 (52.8%) were males, the mean age was 10.23+/-4.945 years. It was found that 117 (93.6%) had poor glycemic control where the mean HbA1c value was11.12 +/- 1.83%. Factors associated with poor glycemic control were duration of diabetes [B 0.2774, (CI 0.0913-0.463) p=0.0038], at most two insulin injections per day [B 1.4304 (0.8594-2.0015) p=0.0001] and Storage of insulin vials in water [B 1.0164 (CI 0.4922-1.5406) p=0.0002]. In the last three months the most common acute complication was hyperglycemia 77 (61.6%) followed by hypoglycemia. Almost all patients with diabetes mellitus have poor glycemic control and factors significantly associated with poor glycemic control were, storage of the insulin in water duration of illness (diabetes mellitus) and frequency of insulin at most two injections per day. On the other hand, hyperglycemia was the common acute complication in the last three months prior to the commencement of the study followed by hypoglycemia, malaria, pneumonia and urinary tract infection