This is a large snake, with females reaching 150 cm in total length (body + tail) and males a little less. Sizes vary among different populations, with M. l. lebetina being somewhat smaller.The head is broad, triangular, and distinct from the neck. The snout is rounded and blunt when viewed from above, which is why it is also called the blunt-nosed viper. The nasal and nasorostral scales are almost completely fused into a single plate, although some variation occurs.The dorsal scales are strongly keeled, except for those bordering the ventrals. M. l. lebetina usually has 146-163 ventral scales. The anal scale is single. The color pattern is less varied than one might expect from a species that is so widely distributed. The head is normally uniformly colored, although it can occasionally be marked with a dark V-shape. Dorsally, the ground color of the body can be gray, brown, beige, pinkish, olive, or khaki. The pattern, if present, is darker. It can be gray, bluish, rust, or brown in color, and may consist of a middorsal row or double row of large spots. When two rows are present, the spots may alternate or oppose, which can produce anything from a saddled to a continuous zigzag pattern. The spots are usually brown, dark gray, or black, but are sometimes red, brick, yellow, or olive in color. Males are usually 1.1 meter in total length, while females may attain a total length of 1.5 m.