OBJECTIVE To detect the expression and transcription pattern of MUC1 in benign and malignant disease, and in two widely studied cell lines, and to investigate the glycosylation of MUC‐1 in bone metastasis of prostate cancer, as mucins have been implicated in the progression and behaviour of several cancers. MATERIALS AND METHODS RNA extracted from cell lines (DU145 and PC3), five samples of BPH and five samples of prostate cancer was reverse transcribed before amplification of MUC1‐specific sequences by polymerase chain reaction. Paraffin‐embedded sections were stained for glycosylated MUC1 and MUC1 core epitopes by HMFG1 and B27.29 antibodies, respectively. Steroid‐treated cell lines werre analysed by fluorescence‐activated cell sorting, using the same antibodies. RESULTS MUC1, in an under‐glycosylated form, was widely expressed in the prostate and in metastatic lesions. MUC1/Z and MUC1/Y RNA were differentially expressed in BPH and prostate cancer, with no detectable expression of splice variant mRNA. This is in contrast to prostate cancer cell line cells (PC3 and DU145), which express splice variant mRNA. CONCLUSIONS BPH, prostate cancer and metastatic prostate cancer all express high levels of under‐glycosylated MUC1. This may explain the inability of previous studies to detect MUC1 in prostate tissue, as the antibody used was specific for a carbohydrate epitope which is not expressed on the under‐glycosylated MUC1.