Abstract: A height adjustable chair includes a user support platform assembly, and posterior and anterior leg assemblies. The user support platform assembly includes first, second, and third platform portions, and a pair of pivot mechanisms. The posterior and anterior leg assemblies include laterally opposed upper leg portions, laterally opposed lower leg portions, and locking mechanisms for locking the lower leg portions in extended relation relative to the upper leg portions. The pivot mechanisms pivotally attach to first platform portion and the posterior leg assembly. The anterior leg assembly is pivotally attached to the posterior leg assembly, the first platform portion, and the third platform portions. The first support platform supports a user thereupon. The anterior and posterior leg assemblies enable the user to vary the height of the first support platform relative to a support surface.