BACKGROUND: The role of the glymphatic system in occult cerebral palsy (CP) remains unclear. In this study, glymphatic system function and its association with motor impairment in occult CP patients was investigated using diffusion tensor image analysis along the perivascular space (DTI-ALPS). METHODS: This retrospective study used DTI to calculate the diffusivity values along the x-, y-, and z-axes in 27 occult CP patients and 27 matched controls. A correlation analysis the ALPS index, derived from perivascular, projection, and association fibres, and with the Gross Motor Function Classification (GMFSC) grade was performed. RESULTS: We found significant differences in the ALPS index between occult CP patients and healthy controls (HCs). The ALPS index of the lateral hemisphere was lower in occult CP patients than in HCs (left: 1.51 ± 0.20 vs. 1.68 ± 0.24, p = 0.011; right: 1.51 ± 0.20 vs. 1.65 ± 0.24, p = 0.019). Correlation analysis revealed a negative correlation between the ALPS index in the lateral hemisphere and the GMFSC grade (left: r = -0.61, p = 0.004; right: r = -0.48, p = 0.015). CONCLUSION: Our findings show that occult CP patients have reduced ALPS indices, suggesting glymphatic system dysfunction. Lower ALPS indices were associated with higher motor function grades, indicating a potential link between glymphatic system dysfunction and motor impairment in CP patients.