The report presents the analysis of 56 pregnant women with hypothyroidism as a consequence of different aetiopathogenetic factor, and 20 healthy pregnant women with normal pregnancies and term deliveries. Patients with hypothyroidism diagnosed prior pregnancy (46) were treated before and during pregnancy with thyroid hormone preparations. Patients with hypothyroidism verified in subclinical form during pregnancy (10) were not treated. In all examined pregnant women the mean values with standard deviations for thyroid-stimulating form hormone levels, total thyroxine and triiodothyronine, in each trimester of pregnancy, free thyroxine and triiodothyronine in the first and the last trimester were recorded; dynamics of their trends, as well as correlation of values in healthy pregnant women were presented. The analysis of the pregnancy course revealed a significantly higher incidence of gestational diabetes mellitus and preeclampsia (p < 0.001). It may be suggested that hypothyroidism is one of the risk factors for development of gestational diabetes, and also one of the pre-existing factors for development of preeclampsia. Delivery occurred in 83.9% of patients; in 12.8% of patients delivery was prior to term while spontaneous abortion occurred in 16.1% of cases (in one third in the first trimester). Similar results were observed in pregnant women with subclinical hypothyroidism. There were 4.2% of stillbirths which corresponded to the rate of perinatal mortality. One infant was born with hydrocephalus and the others were healthy. In the authors' opinion it is necessary to achieve normal metabolic state before pregnancy which should be maintained with substitutional therapy during the whole pregnancy.