Background: Physicians, including psychiatrists and general practitioners (GPs), have been reported as essential sources of stigma towards people diagnosed with a mental disorder (PDMDs), which constitutes an important barrier to recovery and is associated with poorer clinical outcomes. Therefore, psychiatrists and GPs are key populations where it is crucial to examine stigma, improve attitudes and reduce discrimination towards psychiatric patients. Aims: This study is the first to explore mental health-related stigma among Portuguese psychiatrists and GPs, examining the differences between these two specialities and assessing whether sociodemographic and professional variables are associated with stigma. Method: A cross-sectional study was performed between June 2018 and August 2019. A consecutive sample of 55 Psychiatrists and 67 GPs working in Porto (Portugal) filled a 25-item self-report questionnaire to assess their attitudes towards PDMDs in clinical practice. The instrument was designed by the authors, based on previous mental health-related stigma studies and validated scales. The questionnaire includes 12 stigma dimensions ( Autonomy, Coercion, Incompetence, Dangerousness, Permanence, Pity, Responsibility, Segregation, Labelling, Diagnostic Overshadowing, Shame and Parental Incompetence), and its total score was used to measure Overall Stigma (OS). Sample characteristics were examined using descriptive statistics, and the factors affecting stigma were assessed through regression analysis. Results: GPs exhibit significantly higher OS levels than psychiatrists, and present higher scores in the dimensions of dangerousness, parental incompetence, diagnostic overshadowing and responsibility. Besides medical speciality, several other sociodemographic variables were associated with sigma, including age, gender, having a friend with a mental disorder, professional category, agreement that Psychiatry diverges from core medicine and physician’s interest in mental health topics. Conclusions: Our data suggest that both psychiatrists and GPs hold some degree of stigmatizing attitudes towards PDMDs. Overall, these results bring new light to stigma research, and provide information to tailor anti-stigma interventions to Portuguese psychiatrists and GPs.