To compare explicit and implicit stigmatizing attitudes towards mental illness among undergraduate students, medical school students, and psychiatrists, and to assess whether attitudes are associated with education level, exposure to, and personal experience with mental illness. Participants from McMaster University were recruited through email. Participants completed a web-based survey consisting of demographics; the Opening Minds Scale for Healthcare Providers (OMS-HC) 12-item survey, which measures explicit stigma; and an Implicit Association Test (IAT), measuring implicit bias toward physical illness (diabetes mellitus) or mental illness (schizophrenia). A total of 538 people participated: undergraduate students ( n = 382), medical school students ( n = 118), and psychiatrists ( n = 38). Psychiatrists had significantly lower explicit and implicit stigma than undergraduate students and medical school students. Having been diagnosed with mental illness or having had a relationship with someone experiencing one was significantly associated with lower explicit stigma. Mean scores on the OMS-HC "disclosure/help-seeking" subscale were higher compared with the "attitudes towards people with mental illness" subscale. There was no correlation between the OMS-HC and IAT. These findings support the theory that increased education and experience with mental illness are associated with reduced stigma. Attitudes regarding disclosure/help-seeking were more stigmatizing than attitudes towards people with mental illness. The groups identified in this study can potentially benefit from anti-stigma campaigns that focus on reducing specific components of explicit, implicit, public and self-stigma.