Tumour necrosis factor alpha (TNF-alpha) plays a crucial role in host defence against bacterial infections. Summarizing the results, the findings of immunological and clinical research suggest a higher infection risk in rheumatoid arthritis and ankylosing spondylitis patients receiving anti-TNF treatment. This is especially true for granulomatous infections in patients treated with the monoclonal TNF-alpha antibodies infliximab or adalimumab. Furthermore, patients treated with TNF inhibitors have a higher susceptibility to infections because of their higher active and more severe disease. Therefore, patients receiving anti-TNF treatment should be closely monitored for serious infections. A rapid and sufficient treatment of infections that are not mild and transient is recommended. There are atypical signs and symptoms as well as atypical pathogen that should be considered. Patients should be educated about how to avoid infectious complications.