Proximal tibia fractures present a difficult treatment challenge with historically high complication rates. In a prospective study, we asked whether the Less Invasive Stabilization System (LISS) plate can adequately treat extraarticular and complex intraarticular proximal tibia fractures and provide low complication rates and acceptable long-term functional outcomes. We prospectively observed 25 patients with 26 proximal tibia fractures (AO type A2, A3, C1, C2, or C3) treated with the LISS. Consecutive 3-year followup included radiographs and clinical examinations using Knee Society scores and Hospital for Special Surgery scores for extraarticular and intraarticular fractures. No loss of reduction occurred in patients with extraarticular fractures, whereas varus malalignment occurred in one patient with an intraarticular fracture. Two patients with AO 41 C 3.3 fractures had severe knee arthrosis develop and had total knee replacements. The mean Knee Society scores and final average Hospital for Special Surgery scores were similar for extraarticular and intraarticular fractures. Complications related to the surgery included one delayed union and implant removal in two patients. The LISS provided stable fixation of extraarticular and intraarticular proximal tibia fractures and good functional outcomes with a low complication rate. In complex articular fractures additional screws should be used. Level of Evidence: Therapeutic study, Level II (lesser quality randomized controlled trial [eg, < 80% followup, no blinding, or improper randomization]). See the Guidelines for Authors for a complete description of levels of evidence.