Exhibit 99.1

Press Release

COSTCO WHOLESALE CORPORATION REPORTS FIRST QUARTER

FISCAL YEAR 2020 OPERATING RESULTS

ISSAQUAH, Wash., December 12, 2019 - Costco Wholesale Corporation (“Costco” or the “Company”) (Nasdaq: COST) today announced its operating results for the first quarter (twelve weeks) of fiscal 2020, ended November 24, 2019.

Net sales for the first quarter were $36.24 billion, an increase of 5.6 percent from $34.31 billion last year.

Comparable sales for the first quarter fiscal 2020 were as follows:

Total and comparable sales were negatively impacted by approximately one-half percent due to Thanksgiving occurring a week later this year. E-commerce sales in the quarter were negatively impacted by an estimated 12 percentage points.

Net income for the quarter was $844 million, or $1.90 per diluted share, compared to $767 million, or $1.73 per diluted share, last year. This year’s first quarter reflects a $77 million ($0.17 per diluted share) tax benefit related to stock-based compensation, compared to a $59 million ($0.13 per diluted share) similar benefit last year.

Costco currently operates 785 warehouses, including 546 in the United States and Puerto Rico, 100 in Canada, 39 in Mexico, 29 in the United Kingdom, 26 in Japan, 16 in Korea, 13 in Taiwan, 11 in Australia, two in Spain, and one each in Iceland, France, and China. Costco also operates e-commerce sites in the U.S., Canada, the United Kingdom, Mexico, Korea, Taiwan, and Japan.

A conference call to discuss these results is scheduled for 2:00 p.m. (PT) today, December 12, 2019, and is available via a webcast on www.costco.com (click on Investor Relations and “Play Webcast”).

Certain statements contained in this document constitute forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. For these purposes, forward-looking statements are statements that address activities, events, conditions or developments that the Company expects or anticipates may occur in the future. In some cases forward-looking statements can be identified because they contain words such as “anticipate,” “believe,” “continue,” “could,” “estimate,” “expect,” “intend,” “likely,” “may,” “might,” “plan,” “potential,” “predict,” “project,” “seek,” “should,” “target,” “will,” “would,” or similar expressions and the negatives of those terms. Such forward-looking statements involve risks and uncertainties that may cause actual events, results or performance to differ materially from those indicated by such statements. These risks

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and uncertainties include, but are not limited to, domestic and international economic conditions, including exchange rates, the effects of competition and regulation, uncertainties in the financial markets, consumer and small business spending patterns and debt levels, breaches of security or privacy of member or business information, conditions affecting the acquisition, development, ownership or use of real estate, capital spending, actions of vendors, rising costs associated with employees (generally including health care costs), energy and certain commodities, geopolitical conditions (including tariffs), the ability to maintain effective internal control over financial reporting, and other risks identified from time to time in the Company’s public statements and reports filed with the Securities and Exchange Commission. Forward-looking statements speak only as of the date they are made, and the Company does not undertake to update these statements, except as required by law.

CONTACTS: Costco Wholesale Corporation

Richard Galanti, 425/313-8203

Bob Nelson, 425/313-8255

David Sherwood, 425/313-8239

Josh Dahmen, 425/313-8254

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COSTCO WHOLESALE CORPORATION

CONDENSED CONSOLIDATED STATEMENTS OF INCOME

(dollars in millions, except per share data)

(unaudited)

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COSTCO WHOLESALE CORPORATION

CONDENSED CONSOLIDATED BALANCE SHEETS

(amounts in millions, except par value and share data)

(unaudited)