Diabetic ketoacidosis (DKA) may be present at the onset of type 1 diabetes (T1D), increasing both its morbidity and mortality. The aim of this study was to describe the frequency of this complication at the clinical presentation of T1D, as well as possible interfering factors in a multi-ethnic population from Brazil. We have reviewed the medical charts of 545 individuals with T1D diagnosed between 1968 and 2006 from two major local diabetes treatment centers. DKA occurred in 179 patients (32.8%) at the onset of T1D. The frequency of DKA was higher in non-white than white individuals (p<0.0001) and in the younger age groups (<or=5 y/o and 6-10 y/o; p=0.015). The prevalence of DKA at the onset of the disease did not change over the past four decades, except for a higher prevalence in patients diagnosed since 2000 when compared to those that had hyperglycemia detected in the 1990s (p=0.019). To conclude, a significant proportion of individuals present DKA at the onset of T1D in this population, especially very young children and non-white individuals. Unfortunately, the frequency of DKA has not progressively declined in the past decades. An improvement in the educational programs for detection of early signs and symptoms might help to change this scenario.