Although stigma in relation to mental health has been defined as including components of knowledge, attitudes and behaviour, no psychometrically tested instrument to assess behavioural discrimination at the population level has been developed. This paper presents details of the development and psychometric properties of the Reported and Intended Behaviour Scale (RIBS), an instrument based on the Star Social Distance Scale, to assess reported (past and current) and intended (future) behavioural discrimination among the general public against people with mental health problems. Three studies were carried out to evaluate psychometric properties of the RIBS (Study 1, n = 92; Study 2, n = 37; Study 3, n = 403). Adults aged 25-45 in socio-economic groups: B, C1 and C2 (middle-income groups) took part in development and testing of the RIBS. Internal consistency and test-retest reliability is moderate/substantial. Strong consensus validity was found, as rated by service users/consumers and international experts in stigma research. Use of a behavioural outcome may be important to evaluate the effectiveness of interventions intended to reduce stigma and/or discrimination related to mental illness. The RIBS was found to be a brief, feasible and psychometrically robust measure for assessing mental health-related reported and intended behavioural discrimination.