19th century

The áo tứ thân, a traditional four-paneled gown, evolved into the five-paneled áo ngũ thân in the early 19th century.^[6] Ngũ is Sino-Vietnamese for "five." It refers not only to the number of panels, but also to the five elements in oriental cosmology. The áo ngũ thân had a loose fit and sometimes had wide sleeves. Wearers could display their prosperity by putting on multiple layers of fabric, which at that time was costly. Despite Vietnam's tropical climate, northern aristocrats were known to wear three to five layers.

Two women wear áo ngũ thân, the form of the ao dai worn in the nineteenth and early twentieth centuries

The áo ngũ thân had two flaps sewn together in the back, two flaps sewn together in the front, and a "baby flap" hidden underneath the main front flap. The gown appeared to have two-flaps with slits on both sides, features preserved in the later ao dai. Compared to a modern ao dai, the front and back flaps were much broader and the fit looser. It had a high collar and was buttoned in the same fashion as a modern ao dai. Women could wear the dress with the top few buttons undone, revealing a glimpse of their yếm underneath.