An electronic device may be provided with a display. The electronic device may include a housing. A display trim may be formed from injection molded plastic that is molded directly onto the housing. The molded plastic trim may form a rectangular ring around the periphery of the housing. The housing may have angled or curved interior surfaces that are covered by the molded plastic trim. Computer-controlled positioners may be used to center the housing within an injection molding tool. Independently controlled positioners may also be used in capturing the housing between the lower die and the upper die in the injection molding tool. The injection molding tool may inject thermoplastic elastomer material into a channel in the upper die to form the plastic display trim.