An expandable chair includes an extendable seat section which materially extends the width of the main seat section of the chair. When the width of the seat needs to be lengthened, lateral sections are provided which are rotated up from beneath the main center section of the seat and then locked adjacent to the center section. The lateral sections can be rotated down and locked beneath the center section when chair expansion is not desired. Extendable support arms, adjustable outward from the back section of the chair, are provided when the width of the seat's center section is lengthened. These support arms are located behind the back support section and are configured to be slid outward when needed. A unique rack and pinion gear system allows the support arms to be extended and locked in a plurality of lengths.