L-17 inhibitors belong to the group of the most effective and highly safe biological preparations intended for the treatment of psoriasis, and in the case of secukinumab and ixekizumab, also for the treatment of some immune-mediated inflammatory diseases of the joints. Despite initial expectations, they did not prove to be effective for the treatment of non-specific bowel inflammations (IBD). On the contrary, IBD worsening was reported in some cases where IL-17 inhibitors were used, and registration studies were terminated for this indication. In clinical studies, extensive meta-analyses of IL-17 inhibitor use for psoriasis and joint inflammation indications generally did not demonstrate any statistically significant increase in the risk of de-novo IBD with this type of treatment. Data from real-time practice are mostly similar. The literature describes individual cases with an obvious relation of de novo IBD development subsequent to treatment with IL-17 inhibitors in registered indications. The activation of latent, thus far clinically asymptomatic bowel inflammation is usually expected. Therefore, a careful review of medical history focused on bowel problems in personal and family history is necessary before starting therapy with IL-17 inhibitors. We present a similar experience with de novo onset of ulcerative colitis in two patients treated for psoriasis with ixekizumab, with associated psoriatic arthritis in one case.