Intramuscular botulinum toxin A injections are beneficial for the treatment of functional shortening of the iliopsoas muscle, but it is difficult to achieve precise needle positioning and injection. As a solution to this we present an ultrasound-guided injection technique for the iliopsoas muscle using an anterior approach from the groin. The procedure was performed 26 times in 13 patients (seven males, six females; mean age 11 years, SD 9 years 8 months; age range 4 to 31 years), 10 times bilaterally. Indications were functional iliopsoas shortening due to cerebral palsy (17 hips), hereditary spastic paraplegia (four hips), and Perthes disease (five hips). In all cases the iliopsoas muscle was identified easily by ultrasound; the placement of the injection needle and injection into the site of interest were observed during real time. No complications were encountered. Botulinum toxin A (BTX-A) injections have become established as a standard procedure for the treatment of functional shortening of different muscles in persons with spasticity or dystonia (Kessler et al. 1999, Bakheit et al. 2001, Kirschner et al. 2001). Optimal needle placement is essential to avoid severe side effects and to assess lack of response to the drug or incorrect region of injection. While injection into superficial, very palpable muscles is quite easy, the approach to other muscles such as the iliopsoas muscle may be more difficult and the placement of the needle for an optimal injection site is harder to control. As a solution to this, we present an ultrasound-guided injection technique. The main indications for BTX-A injections in the iliopsoas muscle are dynamic hip flexion deformities mostly due to spastic conditions which may compromise walking (increased anterior pelvic tilt during the whole gait cycle, decreased hip extension at terminal stance, increased peak hip flexion during swing; Molenaers et al. 1999. Another indication might be decentration of the femoral head (as part of an injection programme which also includes other muscles like the adductors and the medial hamstrings) for pain relief, reducing care difficulties and, possibly, prevention of further decentration (Porta 2000, Foster et al. 2001, Deleplanque et al. 2002, Lubik et al. 2002). In Perthes disease, BTX-A injections in the iliopsoas muscle and the adductors may prevent a fixed deformity, which is a negative prognostic factor.