Known only from the Ankaratra and Andringitra Massif of central Madagascar, C. hilleniusi is a small chameleon, rarely exceeding 6 inches total length. Originally described as a subspecies of C. brevicornis, it now has specific status. It can be distinguished from C. brevicornis by its smaller size, larger, articulated occipital lobes compared to the headsize on the low, flat casque. C hilleniusi possesses a small, reddish rostral process formed by fusing of the large canthi rostralis which is especially obvious the males.  A dorsal crest composed of widely spaced, enlarged conical scales extends from the neck to at least half the length of the tail. Gular and ventral crests are present but poorly developed. Scalation is heterogeneous. Coloration varies from brownish-gray and mossy green to an off-white and may also include brighter hues of blue,  red, and yellow, particularly in displaying males.

C. Hilleniusi inhabits the scrub and forests, esp. at the forest edges of highland and mountain regions around 1600-2000 meters above sea level. Temperatures may exceed 80-85ºF during the day in the sun and fall to 45-55ºF or even lower at night. Relative humidity is typically high, being 50%-60% during the day and 90% during the night. Rainfall typically exceeds 1,000 millimeters/year.  There is a pronounced rainy season that peaks in December and January.

Caging of this species requires much space, visual isolation and dense foliage as it is active, skittish around keepers, and highly aggressive toward conspecifics. This is very important esp. for pregnant females which became little devils against males if pregnant and males towards their same sex. Large screen areas or a full screen caging is recommended.

A deep night time temperature drop to about low 60`s ºF is essential. A brumation at low temperatures around 53-60ºF should be beneficial to the animals esp. if you want to breed them.  Frequent mistings are also recommended. But let the cage dry out between the mistings. Overall temps should be around 70-75ºF with a basking lamp at one place. Lighting with UV contenting tube lights or halogen lights is highly recommended. Natural sunlight would be best. It accepts most common prey items in right size, esp. flies or waxworms, but if possible it should be provided with netted insects.

Mating includes exagerrated head bobbing and "glowing" of the red nose of the males . Approximately 40 days following copulation eggs are laid in a moist substrate but details of incubation are largely a matter of conjecture. Our own experiences, combined with the knowledge of other high mountain specs like Furcifer campani, which lives at the same regions, a bit higher up at the savannah grassland or the B. xenorhinum from Uganda mountains induces low incubation temperatures around 64-69ºF. A diapause of 6 weeks down to 50ºF after the first 2 month of incubation might be of help. The incubation time should be between 9-12 month. The hatching babies are very small and need very small food items in the first weeks.