Background: Evidence suggests that the majority of people with suicidality do not seek help. Little systematic evaluation of factors influencing professional help-seeking has been done. Aims: To systematically evaluate the factors that influence professional help-seeking for suicidality. Method: Published quantitative and qualitative studies in Medline and PsycInfo databases were reviewed following PRISMA. Results: In all, 55 relevant studies were identified. Of these, 15 studies examined professional help-seeking intentions for perceived suicidal ideation, among people with or without suicidality; 21 studies examined professional help-seeking behavior among people with suicidality; and 19 studies examined suicidal decedents' health services use. Several potential important barriers were identified including high self-reliance, lack of perceived need for treatment, and stigmatizing attitudes toward suicide, toward mental health issues, and toward seeking professional treatment. The presence of suicidality and mental health issues was found to generally decrease help-seeking intentions for perceived suicidal ideation while facilitating actual service use. Social support and informal support from family and friends also played an important role in professional help-seeking. Limitations: Although the majority of the included studies were of sound quality, some of the factors identified in the review were assessed in relatively few studies, and most of the included studies were conducted in industrialized countries. Conclusion: Further quantitative and qualitative studies examining the potential important factors in broader community samples, especially in developing countries, are needed.