X0304 4 2012-03-15 0 0000909832 COSTCO WHOLESALE CORP /NEW COST 0001184948 SINEGAL JAMES D 999 LAKE DRIVE ISSAQUAH WA 98027 1 0 0 0 Common Stock 2012-03-15 4 S 0 16000 D 863367 D Common Stock 942708 I By LLC Common Stock 94772 I By GRAT Common Stock 94772 I By Spouse's GRAT This sale was effected pursuant to a 10b5-1 trading plan. Shares sold as follows: 300 @ 90.3200 600 @ 90.3300 1000 @ 90.3400 1400 @ 90.3500 190 @ 90.3600 200 @ 90.3700 400 @ 90.3800 300 @ 90.3900 500 @ 90.4200 500 @ 90.4500 315 @ 90.4507 400 @ 90.4600 400 @ 90.4700 100 @ 90.4900 300 @ 90.5100 400 @ 90.5104 200 @ 90.5105 100 @ 90.5150 100 @ 90.5200 100 @ 90.5275 200 @ 90.5300 100 @ 90.5350 200 @ 90.5500 300 @ 90.5505 200 @ 90.5600 100 @ 90.5700 300 @ 90.5710 300 @ 90.5800 200 @ 90.5900 100 @ 90.6000 100 @ 90.6150 100 @ 90.6250 100 @ 90.6300 100 @ 90.7000 295 @ 90.7100 100 @ 90.7200 362 @ 90.7300 38 @ 90.7400 100 @ 90.7950 4900 @ 90.8200 Deanna K. Nakashima, attorney-in-fact 2012-03-15