Psoriasis is a chronic inflammatory disease that can affect up to 1% of children. Genetic (family history of psoriasis) and environmental factors (bacterial or viral infections, stress, and trauma) are frequently involved in its occurrence. Napkin psoriasis is a particular form of psoriasis affecting mainly children younger than 2 years of age and can be classified together with other diseases under diaper rash. We present the case of a 4-month-old infant, born at term, naturally, weight and height within the normal range, who was brought to the Dermatology Clinic for the occurrence of erythematosquamous lesions in the anogenital area, buttocks and upper third of the thighs, with subsequent dissemination of lesions. The onset of symptoms began a few days after a respiratory tract infection. Initially he received treatment with systemic antibiotic and topical corticosteroid and antibiotic with unfavorable outcome. Laboratory tests revealed iron-deficiency anemia, leukocytosis, thrombocytosis, accelerated ESR, marked hepatic cytolysis, hyperphosphatemia and nasal carriage of Staphylococcus aureus. A systemic antihistamine and nonspecific desensitization treatment was administered. Topical treatment consisted in the removal of predisposing factors and irritants (diaper, urine) by rigorous hygiene, application of topical non-fluorinated cortico-steroid and use of emollients, with favorable course of the lesions. The peculiarity of the case is that the diagnosis of psoriasis was based on history, physical examination and laboratory tests, in the absence of a pathology examination to confirm the diagnosis. Pathology examination could not be performed due to patient's age as biopsy required general anesthesia.