Transparency is recognised to be a key underpinning of the work of health technology assessment (HTA) agencies, yet it has only recently become a subject of systematic inquiry. We contribute to this research field by considering the Polish Agency for Health Technology Assessment (AHTAPol). We situate the AHTAPol in a broader context by comparing it with the National Institute for Health and Care Excellence (NICE) in England. To this end, we analyse all 332 assessment reports, called verification analyses, that the AHTAPol issued from 2012 to 2015, and a stratified sample of 22 Evidence Review Group reports published by NICE in the same period. Overall, by increasingly presenting its key conclusions in assessment reports, the AHTAPol has reached the transparency standards set out by NICE in transparency of HTA outputs. The AHTAPol is more transparent than NICE in certain aspects of the HTA process, such as providing rationales for redacting assessment reports and providing summaries of expert opinions. Nevertheless, it is less transparent in other areas of the HTA process, such as including information on expert conflicts of interest. Our findings have important implications for understanding HTA in Poland and more broadly. We use them to formulate recommendations for policymakers.