Ewa Kłobukowska (born 1 October 1946) is a former Polishsprinter. She competed at the 1964 Olympics in the 4×100 m relay and 100 m sprint and won a gold and a bronze medal, respectively. She also won two gold and one silver medal at the 1966 European Championships. Kłobukowska set three world records, one in the 100 m (11.1 s, 9 July 1965 in Prague) and two in the 4×100 m relay (44.2 s, 13 September 1964, Lodz and 43.6 s, 21 October 1964, Tokyo). They were annulled by the International Association of Athletics Federations (IAAF) after she failed a gender identification test in 1967, though the test procedures were later found to be inadequate.
Kłobukowska failed a traditional gender test for European Cup women's track and field competition in Kiev in 1967 and was subsequently banned from competing in professional sports. According to the IAAF she had "one chromosome too many". Medical publications revealed that Klobukowska is a genetic mosaic of XX/XXY. If she had been tested one year later at the Mexico Olympics she would have been eligible on the grounds that she was Barr Body positive. Klobukowska has a Barr Body in all of her cells. Athletes without such a Barr Body (inactive X-chromosome) were suspended from competition by 1968 in Mexico City. She gave birth to her son in 1968, and thus must have had a genetic abnormality. Her humiliation led to a change in the gender verification policies by the International Olympic Committee, which from then on kept test results secret.
IAAF erased the three world records set by Kłobukowska, including the two team records in the 4×100 m relay.