Biological medications are effective for the treatment of cancer and inflammatory diseases. The aim of this review is to summarize the available evidence in systematic reviews or meta-analyses about the risk of infection in patients with cancer, arthritis, psoriasis and inflammatory bowel disease who use biological medications. We included systematic reviews or meta-analyses of controlled clinical trials and case/control studies that analyze infections during and after treatment with FDA-approved biological medications for the treatment of cancer, arthritis, inflammatory bowel disease and psoriasis, both in adults and children. The following databases were consulted: PubMed, Epistemonikos, Crochrane reviews, JIB, and Prospero. A quality guideline (AMSTAR) was applied to the selected studies. We included 26 studies. The risk of infections in patients with solid organ cancer is consistent in the literature. In psoriasis there is a risk of non-serious infections. In arthritis and other inflammatory diseases there is a risk of serious infections. In inflammatory bowel disease there is a risk for opportunistic infections. In conclusion, in patients with cancer and inflammatory diseases use biological medications entails a risk of infection. The evidence is different depending on the underlying disease of each patient.