Harriet Kassman, the proprietor of a women’s clothing boutique that helped bring high fashion to Washington and became a shopping destination for designer bridal dresses and inaugural gowns, died Feb. 24 of lung cancer at the Methodist Home in Washington.

Her death was confirmed by her son Nick Kassman. She was 90 but preferred not to reveal her age, she once said, “because I don’t act it and I don’t look it so we don’t have to dwell on it.”

For more than three decades, Mrs. Kassman was considered the District’s unofficial arbiter of haute couture. The Harriet Kassman boutique, located until 2009 in the Mazza Gallerie shopping center, had a loyal stable of elite clients including governmental officials, business executives, and embassy and political wives. Some of them, Mrs. Kassman said, spent six-figure sums annually in purchases.

Mrs. Kassman, who grew up working in her father’s high-end women’s apparel store, had two central insights about Washington women. First, she once told The Washington Post, they are “fashionable but not faddy.” And second, she said, “everybody, at one time or another, likes to look sexy.”

When Mrs. Kassman opened her original location in Friendship Heights in 1977, Washington was considered largely bereft of designer fashion. The city had department stores such as Garfinckel’s, Woodward & Lothrop and Lord & Taylor. But outside of Georgetown, few vendors offered one-on-one service for customers seeking the finest merchandise.

Harriet Kassman, who retired in 2009 after running the Harriet Kassman boutique in the Mazza Gallerie for more than three decades, died Feb. 24. (Marcus Yam/THE WASHINGTON POST)

Mrs. Kassman had worked as a buyer in the Washington area and sought to fill that void, said Ean Williams, the executive director of D.C. Fashion Week. She frequently traveled to New York and Europe looking for new work by designers including Escada, Giorgio Armani, Badgley Mischka and Christian Lacroix. In 1997, then-Post fashion critic Robin Givhan wrote that Mrs. Kassman had “acted as a filter, separating the frippery and the gewgaws from the clothes that have longevity.”

Mrs. Kassman was a slight woman, about 5 feet tall before she stepped into her standard three-inch heels. She favored pearls and fuchsia nail polish. Her store resembled a luxurious house and was furnished with sofas and a chandelier. She greeted her clients at the door (sometimes with her poodle, Bastien) and prided herself on knowing exactly what would suit them for the next black-tie event.

During the recent recession, the Washington gala scene contracted with the economy. Mrs. Kassman closed her store in 2009 and retired.

Harriet Ruth Sussman was born June 24, 1921, in New York, where her father was a tailor for the Bergdorf Goodman department store. In the late 1920s, her parents moved the family to Daytona Beach, Fla., where they opened Sussman’s store.

Mrs. Kassman’s husband of 30 years, Gene Kassman, died in 1984.

Survivors include three sons, Nick Kassman of Rockville, Andrew Kassman of North Potomac and William Kassman of Silver Spring; two sisters; and seven grandchildren.

Mrs. Kassman did not deny the vagaries of her clients’ taste. “Everyone still asks for color,” she told the New York Times, referring to inaugural gowns. “But it seems to me once they have it on, they say to me, ‘Can you order it for me in black?’ ”