Abstract: An adjustable armrest assembly for an ergonomic chair provides for adjustment of the armrests in the forward and rearward direction relative to the front of the chair without inhibiting adjustment of the armrests in other directions. A support frame having one or more rails or rods running perpendicular to the chair front is connected to the seat bottom. The support frame is slidably mounted on the seat bottom to permit sideways adjustment of the width between the chair arms. A support base, to which the chair arm is connected, is slidably supported on the rods. A controller attached to the support frame moves the support base along a line extending from the front to the back of the chair. In one embodiment, the controller includes a gear assembly and a screw drive attached to a manual crank. An expandable linkage is provided between the left and right support member so that both are simultaneously moved while still permitting width adjustment.