Granulomatosis with polyangitis (GPA) is an autoimmune, systemic disease, characterized by necrotizing vasculitis predominantly affecting small vessels. Due to imitating different diseases, a diagnosis of GPA is often difficult. The paper presents a case of 42‑year‑old woman, suspected of tuberculosis or lung cancer, which clearly illustrates the challenge. Only the subsequent development of multiorgan involvement enabled the proper diagnosis. These included skin lesions, affecting of upper and lower airways, gastrointestinal tract, kidneys, general symptoms, elevated inflammatory markers (leukocytosis 24.6 G/l, C‑reactive protein 11.8 mg/dl, procalcitonin 1.16 ng/ml, thrombocythemia 6 2 0 × 10³/l, hyperfibrinogenemia 600 mg/dl), deep anemia with hemoglobin 6.5 g/dl. The diagnosis of severe, generalized GPA was made (BVAS – 33 points, BVAS/WG – 17 points). The remission inducing treatment following the modified CYCLOPS trial regimen was introduced. The remission was quickly achieved (the only persistent symptoms: BVAS – 3 points, BVAS/WG – 2 points, VDI – 3 points). As could be seen from the case, the GPA can have multiple clinical manifestations. Therefore, clinical vigilance to consider the GPA in the differential diagnosis should be maintained by doctors of all specialties.