Health professional education invariably includes clinical field placements as an integral component of professional training in an effort to ensure that knowledge, skills, and behaviour learned about in an academic context are integrated and applied to clinical practice. Significant weight is usually attached to the assessment of competence by supervisors, which typically consists of a structured report rating performance on a number of areas. Such reports are subject to systematic rating biases, particularly leniency and halo errors. Strikingly similar results are observed across disciplines including psychology, social work, nursing, pharmacy and medicine. The leniency bias is typically evident in the reluctance of field supervisors to assign low and fail grades to students on placement. The halo bias is reflected in an overall positive impression of a student who has done well in one competency domain, reducing judgement of true differences between competency domains. Factors contributing this phenomenon may include the small numbers of students on placement at any given time, leaving the supervisor without an ‗anchor‘, and leading to a greater propensity for uncertainty and bias. Secondly, the active face-to-face engagement and intensive supervisor-student interactions over an extended period of time in the field may lead to a relatively close supervisor-student interpersonal relationship that serves to systematically bias supervisor ratings. This study set out to determine the extent of the problems with reliability and validity of supervisor judgments of competency in postgraduate clinical psychology training.