Medullary (solid) carcinoma of the thyroid gland, although first described in 1951, was initially proposed as a clinical entity by Hazard et al1 in 1959. Since that time, 249 cases have been reported in the English literature.2-7 By a review and a statistical analysis of six series, we have investigated the natural history of medullary carcinoma of the thyroid gland. Materials and Methods Physician-authors gleaned data from clinical records for series of cases of medullary carcinoma of the thyroid gland in six medical centers: London Hospital7; Mayo Clinic, Rochester, Minn8; M. D. Anderson Clinic, Galveston, Tex5,6; University of California Hospital, San Francisco3; Cleveland Clinic, Ohio1; and Henry Ford Hospital, Detroit.2 In the ten-year period of reporting, beginning in 1959, the cases totaled 249. From the series as reported, there is no way of ascertaining an overlapping of case studies. Because the several authors stressed