Background Progress testing, a regularly administered comprehensive test of a complete knowledge domain, usually serves to provide learners feedback and has a formative nature. Objective Our study aimed to investigate the acceptability of introducing a summative component in the postgraduate Dutch Radiology Progress Test (DRPT) among residents and program directors in a competency-based training program. Methods A 15-item questionnaire with 3 items on acceptability of summative postgraduate knowledge testing, 7 on acceptability of the summative DRPT regulations, 4 on self-reported educational effects, and 1 open comment item was distributed nationally among 349 residents and 81 radiology program directors. Results The questionnaire was filled out by 330 residents (95%) and 48 (59%) program directors. Summative postgraduate knowledge testing was regarded as acceptable by both groups, but more so by program directors than residents. The transition toward summative assessment in the DRPT was received neutrally to slightly positively by residents, while program directors regarded it as an improvement and estimated the summative criteria to be lighter and less stressful than did residents. The residents’ self-reported educational effects of summative assessment in the DRPT were limited, whereas program directors expected a greater end-of-training knowledge improvement than residents. Conclusions Both residents and program directors support summative postgraduate knowledge testing, although it is more accepted by program directors. Residents receive summative radiological progress testing neutrally to slightly positively, while program directors generally value it more positively than residents. Directors should be aware of these different perspectives when introducing or developing summative progress testing in residency programs.