OBJECTIVE: The hypopharynx has a rich lymphatic network that places patients with tumors of the hypopharynx at high risk for early dissemination of the disease into the cervical lymphatics. Therefore, ipsilateral elective neck dissection of clinically N0 neck in lateralized lesions of hypopharyngeal squamous cell carcinomas (SCCs) is widely accepted as a standard treatment. However, the management of the contralateral N0 neck is still controversial. The aim of this study was to evaluate the incidence and predictive factors of contralateral occult lymph node metastasis in pyriform sinus SCC. MATERIALS AND METHODS: We performed a retrospective analysis of 43 patients with N0 to 3 pyriform sinus SCC with contralateral clinically node-negative necks who had also received contralateral elective neck dissections from 1994 to 2003. Surgical treatment was followed by postoperative radiotherapy in 41 patients. The follow-up period ranged from 4 to 135 months (mean, 40 months). The Kaplan-Meier method and log-rank test were used to calculate the disease-specific survival rates and prognostic significance of contralateral occult lymph node metastasis. RESULTS: Contralateral occult lymph node metastases occurred in 16% (seven of 43) of the subjects. Twenty-six percent of the 27 subjects with clinically node-positive ipsilateral neck developed contralateral occult lymph node metastases, whereas 0% of the 16 subjects with N0 ipsilateral necks (P=.035) developed the disease. Moreover, in cases with primary site extension across the midline, the rate of contralateral occult neck metastasis was significantly higher (P=.010). However, there were no statistically significant differences in age, sex, early versus advanced T stage, number of ipsilateral positive nodes, lymph nodes with extracapsular spread, primary subsite of medial versus lateral pyriform sinus, pyriform sinus apex involvement, and growth type. Patients with no evidence of contralateral nodal cancer had significantly improved disease-specific survival over patients with any pathologically positive nodes (5-year disease-specific survival rate, 66% vs. 33%, P<.05). CONCLUSION: The patients with pyriform sinus SCC with clinically ipsilateral N+ neck and/or extension across the midline are at greater risk for contralateral occult neck metastases. Furthermore, patients who present with a contralateral metastatic neck have a worse prognosis than those staged as N0. Therefore, we advocate bilateral neck treatment in patients with pyriform sinus SCC with clinically ipsilateral node metastases and/or extension across the midline.