Cast and cephalometric analyses were performed to measure the effects of treatment with a lip bumper. The lip bumper was fabricated from an 0.045 inch wire with shrink tubing and no acrylic shields. Nine of the 32 patients were evaluated two years after the comprehensive phase of treatment. Patients were in the mixed dentition stage of development (mean age of 9.9 yrs). A single orthodontist designed all the appliances and treated all the cases. There was significant expansion between the canines, first premolars, second premolars and molars, with the greatest expansion occurring between the first premolars. Cephalometric analysis revealed that the molars underwent angular uprighting but did not move bodily. Incisor irregularity decreased 60% during this phase of treatment. The retention cases revealed that the arch depth decreased, perhaps due to loss of leeway space, but arch widths all were broader, especially in the anterior segment, than at the end of the lip bumper phase. Incisor irregularity also remained trivial (x = 0.3 mm), suggesting appreciable stability.