OBJECTIVE To examine the effects of mastoid and middle-ear volume on the anatomical and functional success of type 1 tympanoplasty in paediatric patients. METHODS This study included 45 paediatric patients who underwent type 1 cartilage tympanoplasty. Patients' demographic data, pre- and post-operative audiological evaluation results, and post-operative graft status were evaluated. Middle-ear and mastoid cavity volumes were calculated (in cubic centimetres) using temporal bone high-resolution computed tomography. Middle-ear and mastoid cavity volume values were compared between patients with and without post-operative anatomical and functional success. RESULTS Anatomical success was achieved in 82.2 per cent of patients (n = 37), and functional success in 68.9 per cent (n = 31). When anatomical success and failure groups were compared, a statistically significant difference was found in mean mastoid volume (p = 0.037), while there was no significant difference in relation to mean middle-ear volume (p = 0.827). The comparison of functional success and failure groups revealed no significant difference in mean mastoid volume (p = 0.492) or middle-ear volume (p = 0.941). CONCLUSIONS The study showed that mastoid pneumatisation volume affects surgical success in paediatric tympanoplasty.