Aim This systematic review and critical evaluation of the literature was conducted to determine how gross muscle morphology and structure are altered in individuals with spastic cerebral palsy (CP). Method Electronic databases were searched for articles describing studies of muscle morphological and structural properties in individuals with spastic CP. Data describing muscle fascicle length, belly length, fascicle angle, cross-sectional area, volume, and thickness were extracted and effect sizes were computed for comparisons between individuals with spastic CP and typically developed individuals, between the paretic and non-paretic side in individuals with hemiplegia for all muscles examined, and across the full spectrum of gross motor function in individuals with spastic CP. Results The final yield consisted of 15 articles that met the inclusion criteria. The main finding of the review was the consistent evidence for reduced muscle belly length, muscle volume, cross-sectional area, and muscle thickness in the comparisons between paretic and typically developed muscle and the paretic and non-paretic muscle across a range of muscles. Interpretation Given the importance of muscle morphology and structure for generating muscle force, it is likely that the observed alterations that occur secondary to the neural lesion in individuals with spastic CP contribute to muscle weakness and the attendant loss of motor function in spastic CP.