Introduction: Recommendations for management of spinal muscular atrophy (SMA) do not contain detailed information about the position of lower limbs during support standing. It has been observed that during the measurement of the range of extension in the hip joint (HE) in SMA patients, the examined limb was often naturally abducted. Aim: The main aim of the study was to compare the values of HE in the sagittal plane and in abduction, and to assess the correlation between the duration of supported standing and HE in SMA patients. Material and methods: The study group consisted of 75 SMA individuals aged 2–22 years and control group consisted of 202 healthy participants. The measurements were performed with the Rippstein plurimeter and goniometer. Results and discussion: Range of HE in SMA patients was larger in abduction than in the sagittal plane. A correlation was noted between the duration of supported standing and HE. Conclusions: Supported standing with hip joint abduction should be used in SMA patients. The obtained results broaden the knowledge about the biomechanics of hip joints in SMA patients.