Introduction: Nephrotic syndrome in children is usually idiopathic and the first episode is rarely observed before the 1^st year of life. Viral infections are a rare cause of this condition. Case report: The paper presents a case of a 9-month-old infant who developed nephrotic syndrome secondary to cytomegalovirus infection. The course of the disease was atypical – not all symptoms of nephrotic syndrome were present; only progressing proteinuria was observed. Proteinuria was preceded by respiratory tract infection with fever. Due to delayed access to serology test results, a combined therapy with glucocorticosteroids and ganciclovir was administered. A rapid remission was obtained. There were no early complications of the therapy and no relapse of nephrotic syndrome. Conclusions: The viral background of nephrotic syndrome should be considered in patients below the 2^nd year of life and when the course of the disease is atypical. Causal treatment can then lead to a permanent and complete remission. This aspect distinguishes this form of nephrotic syndrome from its typical forms affecting the youngest patients – classical forms tend to be steroid-dependent or steroid-resistant.