We aimed to identify factors predicting parametrial invasion in early-stage cervical cancer patients undergoing radical hysterectomy. We recruited women with invasive cervical cancer who underwent radical hysterectomy at a single medical institute from 2000-2011. The clinical and pathological characteristics and outcomes were retrospectively recorded, and the risk factors for parametrial invasion were analyzed. We enrolled 339 patients, including 7 with stage IA1 carcinomas, 10 with stage IA2, 266 with stage IB1, 39 with stage IB2, 14 with stage IIA1, and 3 with stage IIA2. The majority (237/339, 69.9%) had squamous cell carcinoma, while 32 (12.4%) had parametrial invasion. The 16 patients with stage IB1 tumors and parametrial invasion were older (55.9±9.5vs. 49.0±9.9 years, p = 0.005, Mann-Whitney U test), and had deeper cervical stromal invasion (9.59±4.87 vs. 7.47±5.48 mm, p = 0.048, Mann-Whitney U test), larger tumor size (2.32±1.15 vs. 1.74±1.14cm, p = 0.043, Mann-Whitney U test), higher incidences of lymphovascular space invasion (87.5% vs. 28.8%, p<0.001, chi-square test), and greater lymph node metastasis (68.8% vs. 10.8%, p<0.001, chi-square test) than the 260 patients without parametrial invasion. Among the patients with stage IB1 tumor size >2 cm,10% had parametrial invasion and 24.2% had lymph node metastasis compared with only 4% and 9.4% of stage IB1 patients with a tumor size <2 cm, respectively. Only one (0.9%) of the 109 patients aged less than 50 years had parametrial invasion compared with 6 (9.7%) of the 62 patients aged over 50 years. Patients with stage IA2 and IB1 tumors <2 cm may not need radical hysterectomy owing to the low incidence of parametrial invasion.