A human cervical keratinocyte cell line, W12, has been initiated from a low‐grade cervical lesion histologically diagnosed as CIN I. This cell line has, to date, undergone over 300 generations in vitro with an average doubling time of 30 hr: an aneuploid karyotype has developed with progressive in vitro growth. W12 contains HPV16 DNA present at approximately 100 copies and the state of the viral DNA over a number of passages has been examined. The HPV13 DNA is stably maintained at high copy number over several passages and restriction enzyme analysis together with electrophoresis of uncleaved viral DNA indicate that it is present predominantly as the episomal molecule. W12 cells exhibit a typical keratinocyte morphology and, when transplanted into the flank of the nude mouse, form an epithelial lesion with the histological features of CIN I/II.