Background: The incidence and clinical presentation of Type 1 diabetes mellitus (T1DM) varies markedly among countries with a worldwide trend of affected children under-5 years of age. The classical triad of polydipsia, polyuria and weight loss is the most common presentation. Similarly, the frequency of Diabetic Ketoacidosis (DKA) at the onset of T1DM is persistently high in Africa affecting more than two thirds of diabetic children. Objective: To describe the clinical presentation of type 1 diabetes mellitus and factors associated with DKA at presentation among children aged 6 months to 19 years at Muhimbili National Hospital (MNH) in Dar es Salaam, Tanzania. Methods: A hospital based descriptive cross-sectional study was conducted among 134 children and adolescents with T1DM at MNH diabetes clinic. Descriptive statistics such as proportions, means (SD) and median (range) were calculated. Proportions were compared by Chi-square and Fisher's exact tests. Group means for normally distributed variables were compared by Student's t-test whereas non-normal group medians were compared by non-parametric tests (Mann-Whitney-U and Kruskal-Wallis). Regression analyses were done to identify and quantify true predictors of DKA at presentation. Results: Nearly half (46%) of the study participants were diagnosed with DM at the age range of 5 to 10 years and almost a quarter (23%) at the age range of 11-14 years. Most of them presented with classical symptoms of Diabetes i.e. polyuria (95%), polydipsia (93%) and weight loss (79%). Almost 4 out of 10 presented with DKA at the onset of T1DM. Age below 5 years and delayed diagnosis were the factors significantly associated with DKA at onset. Family history of DM and high education level of caretakers were found to be protective factors against DKA at diagnosis of T1DM. Mean duration of symptoms before diagnosis was 3 weeks. However, children who were diagnosed at the age between 11 to 14 years were found to have a relatively longer duration of symptoms. Conclusion: The overall proportion of children diagnosed with DKA at the onset of T1DM was lower compared to previous study in the same hospital. Age below 5 years, delayed diagnosis and low level of education of guardian were found to be significantly associated with DKA in children with newly diagnosed T1DM.