The histological characteristics and extent of tumour spread at the primary site and in the neck are described in a series of 50 patients with a T2 squamous cell carcinoma of the oral tongue. The likely site of origin was lateral tongue in 29 cases and ventral tongue in 21 cases. Simultaneous tumours were evident in four resections and multifocal dysplasia in a further 13. Lymph node metastasis was diagnosed histologically in 27 cases, including one case with bilateral metastases. Comparison of the groups, with and without metastasis, showed significant differences in tumour thickness, tumour diameter, multifactorial histological malignancy grade, vessel invasion and nerve invasion. The number of positive lymph nodes per patient ranged from 1 to 16 (mean 3), and 17 dissections showed spread beyond the nodal capsule. Postoperative follow-up ranged from 1 to 6 years and, at the time of analysis, 18 patients had died of or with disease. Loco-regional failure was related to 'high-risk' features at the primary site and extracapsular spread in the neck.