Abstract: An adjustable mug holder mountable on a vehicle door having different thicknesses of interior sidewall structures includes an inverted generally U-shaped mounting member connected to a side of a cup or mug receptacle which has a two-part base portion which is slidably adjustable over a predetermined range of widths. The mounting member has a free end sized for insertion between a window glass and an interior wall structure of the vehicle door to mount the holder on the wall structure. The base portion is formed by interdigitated channels and fingers in the first and second horizontal members connected to the receptacle and to the free end at approximately a right angle. The A series of holes in one of the channels and a mating post on the associated finger lock the first and second horizontal members in a selected position.