Pyelonephritis in pregnant women is an urgent problem for urology. In the Russian clinical guidelines, there are disagreements on the classification of pyelonephritis. This is probably the cause of its overdiagnosis in pregnant women, as evidenced by the increase in the statistical frequency of pregnant pyelonephritis. This situation is the reason for the unjustified etiotropic therapy of pyelonephritis in this category of patients. On the other hand, the diagnosis of chronic pyelonephritis can cause an underestimation of the severity of the patient’s condition and increase the risk of an adverse outcome of the disease. Along with this, the literature has accumulated data on the absence of a morphological substrate of inflammation during periods of so-called remission, and that pyelonephritis should be considered as reinfection. All this call into question the eligibility of the term chronic in relation to pyelonephritis. In the available literature there are few data on the physiology of the urinary tract in pregnant women. Nevertheless, the accumulated experience indicates the safety of excretory function despite dilatation of the upper urinary tract. In addition, there are no studies indicating the benefits of drainage of both asymptomatic and symptomatic hydronephrosis in pregnancy. All this does not allow associating pregnant pyelonephritis with obstructive in non-pregnant patients, and asymptomatic dilatation of the upper urinary tract should be interpreted as a physiological state.