Objectives Mainstream mental health services are providing more care for individuals with an intellectual disability (ID); this has implications for staff and service users. Attitudes of staff towards people with ID in mental health services may be negative and negative staff attitudes may have a detrimental impact on service provision. Design A cross-sectional design was used. Methods A questionnaire designed to investigate the attitudes and emotions of staff towards delivering mental health care to adults with ID was completed by 84 staff from mainstream and specialist ID services. Results Staff in both services experienced more positive emotions when working with clients whom they are currently employed to work with. When the frequency of contact with adults with ID, the number of individuals worked with and the amount of formal ID training received were considered, there was no significant difference between the attitudes of staff in both services. Positive correlations were found between attitude scores and positive emotional experiences in both services. Conclusions The research suggests that numerous factors, including the role of emotional experience and a number of environmental aspects, need to be considered in the context of providing mental health services to adults with ID to ensure the highest quality. Research limitations and clinical implications of the study are also considered.