In spite of a small size and seemingly localised properties T1 tongue cancer does recur after surgical treatment, locally and/or in regional lymph-nodes, in 30-40% of the patients, and 50% of patients with recurrent disease die because of their cancer. If these patients could be identified by analysis of relevant parameters on the primary biopsy reflecting the biological properties of the tumours more extensive treatment regimes could be given selectively. In 47 primary biopsy specimens from patients with T1N0M0 squamous cell carcinoma of the mobile tongue the aberration in cellular DNA content was significantly higher in the group of tumours which recurred after surgical treatment compared with the non-recurrent group. Tumours in females recurred more frequently than in males. No significant correlation between recurrence and grade of histological differentiation or tumour thickness could be found. Image cytometry DNA analysis provides an objective and reproducible assessment of the nuclear DNA content which could facilitate selection of adequate treatment strategies.