Extramammary Paget's disease (EMPD) is a rare intraepidermal adenocarcinoma that primarily affects the anogenital region. Cases of EMPD reacting with PSA (prostate-specific antigen) have previously been associated with underlying prostate cancer. However, a recent case of EMPD in our department has led us to question the value of PSA as an indicator of underlying prostate cancer. Clinical and pathological data were obtained for 16 cases of EMPD. Formalin-fixed, paraffin-embedded tissue blocks from the primary skin lesions were investigated using PSA and other immunohistochemical markers. 5 of the 16 cases of EMPD stained positive for PSA (2 women and 3 men). However, no reactivity was seen for the prostatic marker P501S. Three of the five patients had been diagnosed with internal malignant disease-two with prostate cancer, stage 1. Immunohistochemical investigations of the tumour specimens from the prostate revealed an immunoprofile which was very different from that of the primary skin lesion. In our study, no cases of EMPD with PSA positivity seem to represent an extension of an underlying prostatic adenocarcinoma. PSA positivity can be seen in cases of EMPD without associated adenocarcinoma of the prostate.