OBJECTIVE: To report abnormal changes in lower leg anterior compartment pressure in 1 subject who consumed creatine as a dietary supplement. BACKGROUND: The subject received creatine at a dosage of 0.3 g.kg body mass(-1).d(-1) for 6 days, followed by 0.03 g.kg body mass(-1).d(-1) for 28 days. Thereafter, the subject consumed no supplement for 21 days. Compartment pressure was measured pre-exercise and for 15 minutes postexercise after a treadmill run for 20 minutes at 80% of VO(2) max before supplementation and after 6 and 34 days of supplementation. DIFFERENTIAL DIAGNOSIS: Normally, resting anterior compartment pressure is less than 15 mm Hg, whereas postexercise pressure is below 30 to 35 mm Hg. Creatine supplementation for 6 days dramatically increased pressure at rest (31 mm Hg) and at 1 minute (67 mm Hg), 5 minutes (35 mm Hg), 10 minutes (28 mm Hg), and 15 minutes (26 mm Hg) postexercise. Pressure remained high at rest (35 mm Hg) and at 1 minute (109 mm Hg), 5 minutes (90 mm Hg), 10 minutes (87 mm Hg), and 15 minutes (69 mm Hg) postexercise after 34 days of supplementation. TREATMENT: The subject stopped taking creatine for 21 days. Compartment pressure was measured at rest and after exercise after 7 and 21 days with no supplementation. Anterior compartment pressure decreased after cessation of creatine supplementation. However, pressures were elevated at 7 days postsupplementation at rest (26 mm Hg) and at 1 minute (112 mm Hg), 5 minutes (58 mm Hg), 10 minutes (40 mm Hg), and 15 minutes (30 mm Hg) postexercise. Pressures at 21 days postsupplementation remained high at rest (24 mm Hg) and at 1 minute (64 mm Hg), 5 minutes (42 mm Hg), 10 minutes (27 mm Hg), and 15 minutes (27 mm Hg) postexercise. CONCLUSION: These data indicate that creatine supplementation can substantially increase anterior compartment pressure in the leg.