We report the cases of two patients who developed eruptive cutaneous squamous cell carcinomas (SCC) soon after commencement of ustekinumab, as treatment of moderate to severe plaque type psoriasis. Ustekinumab is a human monoclonal antibody with a novel mechanism, selectively targeting the shared p40 subunit of interleukin-12 (IL-12) and IL-23. Its efficacy has been well documented in three large phase-III trials (PHOENIX I, PHEONIX 2, ACCEPT). Safety data on this new biological agent continue to grow. To date, no link between ustekinumab and cutaneous carcinogenesis has been demonstrated and, to our knowledge, these cases are the first of their kind. Importantly, both these patients had independent risk factors for developing non-melanoma skin cancers; however, the specific time correlation with the administration of ustekinumab is of note. Our report suggests that ustekinumab may allow the development of cutaneous carcinomata in predisposed individuals.