When a Manhattan restaurant has been in business for 20 years, when its old customers clue newcomers in on what to order and even have wall plaques over their favorite tables, it’s obviously special. Seeda Thai II, which serves authentic, sometimes-exotic Thai and Vietnamese cuisine, is such a place. Many diners have been going to it from the beginning.

And those plaques have more than just names on them—they show the menu’s code numbers for the dishes the regulars order. For instance: “SP1” for Chef’s special one—a peanut chicken that’s a skinned chicken breast escorted by subtle basil fried rice and a lip-smacking sauce made from ground peanuts.

Seeda started out as a Thai restaurant, but when the long-running show Miss Saigon opened near by in 1991 it added a Vietnamese menu. The show has since closed, but Seeda is still open and perking along at a healthy pace.

From the outside, this Broadway area storefront isn’t a big, impressive spot. It could easily be passed by (that would be a mistake). Inside it’s a different story; though not impressive, it’s authentic, charming and cozy with its Thai Batik wall decorations, tropical fish aquarium and mannequin dressed in traditional Thai garb. Patrons sit beside brick walls at candle-lighted tables under trac lights and a skylight with hanging plants.

If long time patrons fail to make suggestions owner Janet Jarusuk is very helpful. We listened to her and her valued regulars, read the wall plaque and menu, and ordered appetizers like hot and sour soup, steamed dumplings, mee krob and Thai salad. Entrées, aside from the peanut chicken, were nam, sweet-and-sour duck, and vegetable pad Thai.

Although I enjoyed some dishes better than others, there wasn’t a clunker among them. A few of the selections sound like typical Chinese fare and are Chinese influenced, but they aren’t the same dishes. That hot and sour soup for instance, is called Tom yum and is studded with shrimp in citrusy lemongrass broth. The Thai salad with greens and tofu has a peanut dressing you’ll never find in a Chinese restaurant. Even the familiar steamed pork dumplings have some desirable Thai snap to them.

Mee krob, one of Thailand’s two most popular dishes, (the other is Pad Thai), with crisp, discretely sweet and sour noodles and a mix of bean sprouts, shrimp and pork is a triumph. So is nam, an artfully-assembled mélange of minced pork, ginger, onion, chili, and lime juice. Meat and sweet ingredients aren’t among my favorite combinations, but the half-sweet and sour duck here, with its blend of crisp, skinned, moist meat, pineapples, tomatoes, and chili sauce with cashews was an exception. Just as Seeda itself is exceptional.

309 W. 50th St. btw. Eighth & Ninth Aves., 212-586-4040.

Richard J. Scholem is a former contributor of restaurant reviews for the Long Island Section of The New York Times.