Background Equal access to mainstream healthcare services for people with intellectual disabilities (ID) still requires attention. Although recent studies suggest that health professionals hold positive attitudes towards people with ID, stigmatising attitudes may influence their efforts to serve people with ID in community healthcare practice. To stimulate inclusion in mainstream healthcare services, this systematic review focussed on barriers in attitudes of mainstream health professionals towards people with ID. Method Five electronic databases were systematically searched and references in full text articles were checked for studies published in the English language between January 1994 and January 2016. A social-psychological triad of cognitive, affective and behavioural dimensions of stigmatising attitudes is used to structure and discuss the results. Results The literature search generated 2190 records with 30 studies that passed our exclusion criteria. Studies were mostly cross-sectional and of moderate quality. With respect to stigma, a lack of familiarity with and knowledge about people with ID was found. ID was considered as a stable condition not under personal control. Moreover, mainstream health professionals had either low or high expectations of the capabilities of people with ID. Professionals reported stress, lack of confidence, fear and anxiety, a tendency to treat people with ID differently and a lack of supporting autonomy. Conclusions Stigmatising attitudes towards people with ID appeared to be present among mainstream health professionals. This might affect the ongoing challenges regarding inclusion in mainstream healthcare services. To facilitate inclusion in mainstream healthcare services, it is recommended to include contact and collaboration with experts-by-experience in education programs of health professionals. Future research should progress beyond descriptive accounts of stigma towards exploring relationships between cognitive, affective and behavioural dimensions as pointers for intervention. Finally, inclusion would benefit from an understanding of equal' treatment that means reasonable adjustments instead of undifferentiated treatment.