Thyroid disease is common in pregnancy and is associated with miscarriage, preterm delivery and postpartum thyroiditis (PPT). Systemic lupus erythematosus (SLE) is associated with miscarriage and preterm delivery. The hypotheses of the study are (1) pregnant women with SLE will have a high prevalence of undiagnosed hypothyroidism and a high prevalence of PPT, and (2) women with SLE and thyroid disease will have an increased incidence of adverse pregnancy outcomes as compared with pregnant women with SLE who do not have thyroid disease. This was a retrospective study of the Hopkins Lupus Cohort. All women had thyroid-stimulating hormone and thyroid antibodies assayed on frozen sera. In total, 63 pregnant women who met the ACR classification for SLE were evaluated. Outcome measures were the prevalence of thyroid disease during pregnancy and postpartum, and pregnancy outcomes. Some 13% of the women were on thyroid hormone prior to becoming pregnant, 11% were diagnosed with hypothyroidism during pregnancy, and 14% developed PPT. The prevalence of preterm delivery was 67% in women with thyroid disease and 18% in women who were thyroid disease free (p = 0.002). The presence of thyroid antibodies was not correlated with preterm delivery. Pregnant women with SLE have an increased prevalence of thyroid disease. Women with SLE and thyroid disease have an increased prevalence of preterm delivery.