The present study aimed to investigate the effects of botulinum toxin injections to the iliopsoas combined with physical therapy on gross motor functions in patients with cerebral palsy. This retrospective study consisted of 80 subjects diagnosed with cerebral palsy associated with diaplegia, who were randomly divided into two groups: the experimental group (n=40) and control group (n=40). Subjects in the experimental group were treated by physiotherapy along with injection of 48-100 U botulinum toxin type A (Botox, Allergan) in the neuromuscular junction of the iliopsoas, whereas subjects in the control group received physiotherapy alone. Gross motor changes were evaluated using Gross Motor Function Measurement Scale (GMFM), and muscle spasm was evaluated by the Ashworth Scale and hip joint angles before the treatment and 3 days, 7 days, 1 month, 2 months and 3 months post-treatment. Data were analysed using the one-way ANOVAL test (P<0.05). The results demonstrated an increase in the scores of GMFM in both groups following intervention; however GMFM scores were significantly increased in the experimental group (P<0.01). Significantly increased hip angles and decreased iliopsoas muscle spasms were detected in the experimental group (P<0.05). In conclusion, the present study demonstrated that botulinum toxin type A injection to the iliopsoas muscle combined with physiotherapy was an efficient method of treatment for cerebral palsy patients with diaplegia.