The aim of this study was to examine the reasons why primary care doctors undertake postgraduate diploma studies in a mixed private/public Asian setting. Twenty four past or current postgraduate diploma students of the family medicine unit (FMU) of the University of Hong Kong participated in three focus group interviews. A structured questionnaire was constructed based on the qualitative data collected and was sent to 328 former applicants of postgraduate diploma studies at FMU. "Upgrading medical knowledge and skills" and "improving quality of practice" were two of the factors that most of the respondents considered to be significant in motivating them to undertake postgraduate diploma studies. "Time constraint" and "workload in practice" were however the most significant demotivating factors. Financial issues were more seriously considered by the junior than the senior doctors. To be able to "expand patient base and/or number" was considered to be a significant factor by the private doctors who were also keen to "improve communication and relationship with patients". These findings suggest that there are mixed reasons for primary care doctors to undertake postgraduate diploma studies. Course organisers should take into consideration these various reasons in planning their programmes.