A 10m multistage shuttle swim test (MSST) was designed for the assessment of aerobic fitness of competitive water polo players. Test-retest reliability was determined using a sample of 22 female and 22 male trained water polo players. An intraclass correlation coefficient of 0.99 (p>0.05) was calculated between the two test scores. The technical error of measurement for the test was 2.3 shuttles or 5.0%. The validity of the test was determined using a sample of 13 female and 12 male water polo players. A validation correlation coefficient of 0.88 resulted between the number of shuttles completed during the MSST and VO2max [litres/body surface area/ minute (l x BSA-1 x min-1)] measured during an incremental tethered swim test to exhaustion. A stepwise multiple regression revealed that VO2max (l x BSA-1 x min-1) accounted for approximately 78% of the MSST variance. It was concluded that the 10m multistage shuttle swim test is a reliable and valid field test of aerobic fitness for use with trained water polo players.