Immunotherapy with immune checkpoint inhibitors (ICIs) was shown to improve survival of patients with solid tumors such as: melanoma, renal carcinoma, non-small cell lung cancer, cutaneous carcinomas, or head and neck carcinoma. However, a special type of ICIs toxicity is observed, namely noninfectious inflammation of different organs associated with autoimmunity known as immune‑related adverse events (irAEs). This noninfectious inflammation may affect the endocrine system, gastrointestinal tract, heart, skin, and nervous system. The lungs are also often involved and this condition is referred to as checkpoint inhibitor pneumonitis. The toxicity of ICIs is graded from 1 to 5 depending on the clinical course, 5 being a fatal complication. Corticosteroids are the treatment of choice, generally with good efficacy. In some difficult cases, escalation of immunosuppression is required. Knowledge of irAEs should be promoted among clinicians of all specialties, nurses, patients and their families. The aim of this review is to present the wide spectrum of irAEs: clinical signs and symptoms, differential diagnosis, diagnostic procedures, and treatment. Data are supported by our own clinical observations.