Abstract: An adjustable office chair (10) comprises a base assembly (12), a seat assembly (14) and a backrest assembly (16). The seat assembly (14) is horizontally rotatable on the base assembly (12) and is raised and lowered thereon by a manually controlled pneumatic actuator (24) connected between the base and seat assemblies (12, 14). The seat assembly (14) comprises a lower seat frame (50) which is mounted on the piston rod (28) of the pneumatic actuator (24) for horizontal rotation and an upper seat frame (52) which is mounted for vertical pivotal movement on the lower seat frame (50). A seat pan (54) is movably mounted on the upper seat frame (52) and is manually movable to selected attitudes wherein it is automatically releasably latched by a mechanism (56).