The UK Breast Screening Programme has recently expanded the age range for invitation in the prevalent round to 70 years. In contrast, fewer radiologists now choose to specialise in the area of breast cancer screening. In response to this depletion in film-reading personnel, an increasing number of radiographers have been trained as advanced practitioners in order to film-read alongside the current radiologists. As part of the quality assurance programme for the National Health Service Breast Screening Programme (NHSBSP), each film-reader can participate in a voluntary self-assessment scheme (Personal Performance in Mammographic Screening, PERFORMS) which consists of a number of recent challenging breast screening cases that are amassed nationally and distributed bi-annually. The scheme produces anonymous data on any areas of difficulties that individual participants have; these data can then be aggregated over groups of participants or over specific types of screening cases. In this paper, the areas of difficulty experienced by groups of advanced practitioners and radiologists on the PERFORMS cases were investigated to determine whether there were occupational group differences in reading skills in terms of case classification and feature type. Identifying if such problematic areas exist would be the first step to provide training sets specially tailored to the needs of particular occupational groups. As a bench mark for which cases could be problematic, the types of cases that a panel of experienced radiologists deemed as difficult was first examined in order to compare the performance of both film-reading groups against this panel standard. Secondly, any differences in performance error and case characteristics (classification, difficulty level and feature type) between radiologists and advanced practitioners were examined. The decisions of 15 experienced “panel” radiologists and approximately 400 film readers (including radiologists and advanced practitioners) were compared on 180 cases, over a number of years. This study employed a matched design which controlled for any differences between radiologists and advanced practitioners in terms of real-life factors, such as volume of cases read per week and years of radiological experience. The results elucidate the type of cases most appropriate for advanced mammographic training. No significant differences were found between the advanced practitioners and radiologists on these self-assessment screening cases, indicating that dedicated occupational group training is not required.