Abstract: A chair having height-adjustable arm assemblies respectively mounted adjacent opposite sides of a seat. Each arm assembly includes a horizontally elongate armrest connected to an upper end of an arm upright. The arm upright includes a vertically oriented support segment which has a guide bore defined therein. The armrest includes a vertically elongate slide tube and a horizontally elongate arm element connected to an upper end of the slide tube. A lower end of the slide tube is movably mounted within the guide bore. A lock arrangement functions to permit the slide tube to be positioned relative to the support segment at any one of a plurality of height positions. The lock arrangement includes a cartridge assembly that has a gear which is rotatably supported and carried by the slide tube. The gear has a plurality of gear teeth which engage with a series of vertically spaced notches defined within the support segment.