There have been reports that squamous cell carcinomas (SCC) and basal cell carcinomas (BCC) are surrounded by continuous epithelial basement membranes (EBMs). This argues against the hypothesis that EBM breaks are required for tumour invasion. We have used morphometric techniques to re-examine the evidence for SCCs and BCCs as objectively as possible. We assessed sections stained for type-IV collagen from 12 SCCs, 14 keratoacanthomas (KAs), 9 morphoeic BCCs, 10 nodular BCCs and 7 superficial multifocal BCCs. In the centre of these tumours, the EBM was generally more continuous than at the periphery, and this difference was statistically significant for SCCs, KAs and morphoeic BCCs (p < 0.01 in all). By considering central and peripheral tumour regions separately, a significant difference was seen between SCCs and the difficult to distinguish benign tumour KA. In the centre of the KAs, EBM was significantly more continuous than than in SCCs (p = 0.0029), which may suggest new ways of distinguishing these lesions. All of the SCCs and morphoeic BCCs examined showed clear evidence of EBM breaks, but some nodular BCCs did not. As nodular BCCs show an expansile growth pattern without typical histological features of tumour invasion, we suggest that these tumours may be at a pre-malignant stage. In general, our findings are consistent with the hypothesis that EBM breaks are required for tumour invasion.