Confidence in identifying different diagnostic categories of mental disorders by general health workers who provide the bulk of Papua New Guinea's (PNG) mental health care is vital for the country's provision of mental health care. Making a psychiatric diagnosis is complicated by PNG's diverse culture and estimated 800 distinct languages. These cultural-linguistic factors influence help-seeking behaviour and continued use of traditional treatment despite the introduction of western approaches to mental health care. The aim of this study was to determine the confidence of health workers in identifying and diagnosing different categories of mental health problems in this complex environment. A sample of 209 Papua New Guinea health workers from four geographic regions completed a questionnaire that assessed background levels of training and confidence in diagnosing a range of modern and culture specific diagnoses. Overall, respondents reported relatively little prior mental health training. Consistent with this were the relatively low levels of confidence for culture specific diagnoses (e.g. sorcery), but significantly higher levels of confidence with modern diagnoses (e.g. depression). The implications of the findings for training and provision of mental health care are discussed.