Background: The incidence of diabetes mellitus is ever increasing. Individuals with diabetes mellitus may have concurrent mental health disorders and are shown to have poorer disease outcomes. The objectives of this study were to determine the prevalence of depression, anxiety and stress (DAS) in diabetes patients aged 20 years or more in the primary care setting. Methods: This was a cross-sectional study involving the use of self-administered questionnaire conducted in eight primary care private and government clinics in Pulau Pinang and Melaka, Malaysia. The validated DASS-21 questionnaire was used as a screening tool for the symptoms of DAS. Prior permission was obtained from the patients and, clearance from ethical committee was obtained before the start of the study. Data analysis was done using SPSS statistical software. Results: A total of 320 patients with diabetes from eight centres were enrolled via convenience sampling. Sample size was calculated using the Kish’s formula. The prevalence of DAS among patients with diabetes from our study was 26.6%, 40% and 19.4%, respectively. Depression was found to be significantly associated with marital status and family history of DAS; anxiety was significantly associated with monthly household income, presence of co-morbidities and family history of DAS; and stress was significantly associated with occupation and family history of DAS. Conclusions: The prevalence of DAS was higher in patients with diabetes compared with the general community. We recommend to routinely screen all patients with diabetes using the DASS-21 questionnaire because it is easy to perform and inexpensive.