Hydrometra in the mare is a condition given little attention in the veterinary literature. Defined as "an accumulation of watery or mucoid fluid in the uterus," hydrometra can be used interchangeably with the term mucometra, and should be considered in the differential list for causes of uterine enlargement along with pyometra, pregnancy and pneumo-uterus. There are multiple suggested etiolgies for hydrometra, some of which are not very well described. Both physical (congenital and acquired) and functional abnormalities may be responsible for the development of hydrometra, and a thorough obstetrical exam is required to elucidate the etiology. This paper reports on a miniature mare with hydrometra, secondary to physical complications resulting from an earlier dystocia, diagnosed by transrectal ultrasonography and vaginoscopy.