To determine the frequency of hyponatremic complications during hysteroscopic myoma resections using sorbitol-mannitol distending medium and its relationship to operative time, fluid balance, and myoma size, we reviewed all operative hysteroscopic procedures performed by the Section of Reproductive Endocrinology and Fertility at Yale-New Haven Hospital over a 1-year period during which that medium was used. Twenty-six cases were identified of which seven involved hysteroscopic myoma resections. Hyponatremia occurred in four of the seven patients, and in one it was associated with severe posttransurethral prostatic resection (post-TURP) syndrome. The degree of hyponatremia varied roughly in direct proportion to fibroid volume and fibroid volume as a percentage of uterine volume. No relationship was found between the degree of hyponatremia and operating time, estimated submucosal volume, and uterine volume. We conclude that dilutional hyponatremia and the post-TURP syndrome may occur with the use of sorbitol-mannitol distension medium during hysteroscopy. They occur more frequently during operative hysteroscopy to resect myomata, with myoma size and myoma volume expressed as a percentage of uterine volume possibly influencing the degree of hyponatremia.