One of the dilemmas in behavioural assessment is the extent to which both specific functional analyses and more general case formulations are dependent on professional judgement and thus subject to bias. While in theory the functional analysis represents hypotheses about controlling variables which can then be subjected to empirical test, the clinical reality is that many such hypotheses are only loosely evaluated, post-hoc, by virtue of the success, or otherwise, of treatment. The role of cultural variables in the development and testing of hypothesised functional relationships is thus particularly difficult to evaluate. This paper suggests guidelines for evaluating the cultural context of behavioural assessment in clinical practice. The proposed criteria are seen as having relevance in assessing clients of both dominant and nondominant cultures. In Aotearoa / New Zealand these issues are examined within a bicultural framework. Legal and moral imperatives defining a partnership between two peoples mandate additional considerations for sound clinical assessment. The practical implications of these issues for ensuring a culturally sensitive application of behavioural assessment principles are examined according to psychometric standards, principles of behaviour change, and ethics.