The Test of English as a Foreign Language (TOEFL) measures the English language proficiency of foreign students who apply for higher education in the United States. It is administered according to a strict schedule through the International and Special Center (I&SC) testing program or at ad hoc intervals by institutional users as part of the TOEFL Institutional Testing Program (INST). This study investigated the patterns of test taking and score change for examinees who repeated the TOEFL in an International or I&SC administration within 24 to 60 months after initial testing. Data for examinees who repeated TOEFL within 1 to 12 months following initial testing by institutions participating in the TOEFL INST were also analyzed. In both the I&SC and INST samples, TOEFL repeaters registered substantial average net gains in performance. Findings suggested that there may be differences among national-linguistic groups in typical rate of acquisition of proficiency in English. The magnitude of the average score changes found to be associated with test repetition for repeaters, combined with relatively strong differences among national-linguistic groups in both incidence of test repetition and mean score change, indicates that for purposes of summary reporting on TOEFL performance (e.g., in defining basic reference groups), it is important to specify the test-repetition status of the gorups of examinees involved. (JAZ)