Isthmocele has been implicated as a causal factor in patients with secondary infertility. We aimed to investigate the diagnostic effect of saline infusion sonography using solid embryo transfer catheter in patients suffering from secondary infertility. Materials and Methods: Sixteen patients who applied for infertility evaluation at the Center for Human Reproduction and Infertility of Ankara University and were suspected to have isthmocele on standard vaginal ultrasonographic evaluation were enrolled in the study. All patients were then subjected to saline infusion sonographic evaluation to confirm the diagnosis and measure the base width and area of the isthmocele, and myometrial thickness if confirmed. Results: The mean age of the patients was 37.7±3.7, mean gravida was 2.7±1.4, and mean parity was 2.0±0.8. The mean procedure time was 4.1±1,1min. Among the patients, 13 underwent one previous cesarean section, and three experienced two cesarean births. The mean duration of secondary infertility was 19.18 months. Apart from infertility, 10 patients (62.5%) suffered from intermenstrual bleeding, eight (50%) suffered from prolonged bleeding, and six suffered from mucous discharge (%37.5). The mean measured isthmocele base width was 5.6±1.6 and 10.1±2.4 mm (p<0.001), isthmocele area was 21.2±5.2 vs. 38.7±10.2 mm2 (p<0.001), and residual myometrial thickness was 5.4±2.5mm and 4.8±2.1mm (p=0.49) before and following saline infusion sonography respectively. Conclusions: The contours and area of isthmocele and residual myometrial thickness can be more clearly depicted by saline infusion sonography, especially in patients with a suspicious diagnosis during routine transvaginal ultrasound examination. Saline infusion sonography using an embryo transfer catheter is a safe and easy procedure that may aid in the diagnosis of isthmocele and in tailoring the optimal treatment approach in patients suffering from secondary infertility.