An unusual case of acute axillary vein compression secondary to hypertrophy and intramuscular edema of the subscapularis muscle is described in a competitive swimmer. The signs and symptoms of this condition are similar to those of axillary vein thrombosis, including nonedematous swelling, discoloration, pain, and prominent cutaneous veins of the involved upper limb. Early recognition and diagnosis by means of venography are important to distinguish the condition from axillary vein thrombosis and to alert the practitioner to the potential of future axillary vein thrombosis in such a case. The treatment is primarily conservative.