Objective: The incidence of bilateral testicular germ cell tumours (TGCT) is low and constitutes 0.5%-7% of all testicular tumours. We aimed to evaluate the clinical and pathological features of unilateral and bilateral TGCT, as well as prognostic factors in bilateral cases that may have an impact on oncological outcomes. Materials and Methods: Bilateral TGCT were detected in 10 (11.4%) of 87 patients between January 2010 and July 2016. Patients with 68 unilateral and 10 bilateral tumours (4 synchronous, 6 metachronous) had completely accessible data. We retrospectively evaluated their clinical-pathological data and postoperative follow-up results. Results: Four patients with bilateral synchronous tumours had a seminoma and three (75%) of them had a stage III disease. At a median follow-up of 31.50 (29-37) months, local recurrence, distant metastasis and death were observed in two patients with stage III disease. No recurrence or metastasis was seen in six patients with unilateral TGCT at 33 (24-50) months of follow-up, but metachronous tumours occurred in the contralateral testicles. At a median follow-up of 25 (11-39) months after metachronous tumour development, local recurrence, distant metastasis and death were observed in the contralateral testis of patients with stage III disease. There was no significant difference in bilateral and unilateral cases for disease-free survival, progression-free survival (PFS) and overall survival (OS). PFS and OS were significantly shorter (p=0.039) in bilateral synchronous tumours than in metachronous tumours. Moreover, stage III disease was more common (75% vs 33.3%) in synchronous tumours. Family history (OR: 6.556, p=0.035), testicular dysgenesis syndrome (OR: 3.876, p=0.031), disorders of semen parameters (OR: 2.879, p=0.037), undescended testis (OR: 2.561, p=0.026), monocyte/lymphocyte ratio >0.31 [odds rotio (OR): 2.234, p=0.022], testicular microlithiasis (OR: 2.015, p=0.015) and neutrophil/lymphocyte ratio >3.23 (OR: 1.348, p=0.025) increased the risk of contralateral tumour development. Conclusion: Bilateral synchronous tumours are detected at a more advanced stage and have lower PFS and OS durations, but survival rates are similar to those of unilateral tumours. Long-term follow-up is necessary for patients with unilateral TGCT having certain risk factors due to the possibility of metachronous tumour development in the contralateral testis.