A significant correlation between thyroid function and purine nucleotide metabolism has been established in hypothyroidism. On the contrary, the relationship between hyperthyroidism and purine metabolism is more controversial. The present study evaluates the prevalence of hyperuricemia and gout in patients affected by primary hypothyroidism and hyperthyroidism. We studied 28 patients with primary hypothyroidism and 18 patients with primary hyperthyroidism, all hospitalized because of endocrine dysfunction. All underwent a series of clinical, biochemical and instrumental evaluations; in particular, thyroid-stimulatin hormone (TSH), free thyroxine (fT4), blood urea, serum creatinine, creatinine clearance, serum and urinary uric acid levels were measured. In comparison to the prevalence reported in the general population, a significant increase of both hyperuricemia and gout was found in the hypothyroid patients, and of hyperuricemia in the hyperthyroid patients. In hyperthyroidism the hyperuricemia is due to the increased urate production, while in hypothyroidism the hyperuricemia is secondary to a decreased renal plasma flow and impaired glomerular filtration. Ourfindings confirm the data in the literature concerning the high prevalence of hyperuricemia and gout in hypothyroidism. It shows that hyperthyroidism can cause a significant increase in serum uric acid, as well, although lower than the hyperuricemia due to thyroid hormone deficiency.