This feasibility study describes the development and application of a new intensive treadmill locomotor training program for young children with cerebral palsy (CP). The premise is that early, intensive, and task-specific locomotor training initiated even before independent walking is attained will promote improved locomotor skills. Four children, three girls and one boy, with spastic cerebral palsy (age range: 1.7–2.3 years) received a combination of conventional therapy and treadmill training four times per week for four months. To enable treadmill locomotor training, a customized treadmill capable of very low speeds and with several safety features, including a harness that could also be used for weight support, was custom built. Change in locomotor performance was evaluated with three clinical measures: the Gross Motor Function Measure (GMFM), a gait videographic test and the Supported Walker Ambulation Performance Scale (SWAPS). In addition, a full laboratory gait analysis was performed at baseline and at two and four months posttherapy. The results confirm the feasibility of early and intensive treadmill locomotor training in young children with CP even before independent walking is attained. Gait spatiotemporal parameters and the GMFM total score did not reveal changes observed in the video records by trained observers while laboratory gait evaluations were confounded by the poor locomotor capacity, especially at baseline. The GMFM D and E subscore and the SWAPS, were more sensitive to changes in the supported locomotor status and may be more appropriate than the GMFM total score for future studies requiring the matching of children who are nonindependent walkers. The results of this study pave the way for additional work on the SWAPS or for future efficacy trials using treadmills.