We describe a female patient with insulin-dependent diabetes mellitus and autoimmune thyroiditis. Transient hyperthyroidism developed in the postpartum period in two successive pregnancies, followed by temporary hypothyroidism with eventual full recovery. The clinical course was consistent with "silent thyroiditis" and the circumstantial evidence suggested that alterations in the antibody titers due to pregnancy may have been responsible for these episodes. This case study serves to emphasize that hyperthyroidism and hypothyroidism in the postpartum period may be transient, and this fact should be considered in therapeutic management of such a patient.