From 1977 to 1990, 94 evaluable patients were treated with iridium-192 implantation in the Centre Claudius Regaud for a Stage I (52 patients) or a Stage II (42 patients) squamous cell carcinoma of the mobile tongue and/or the floor of the mouth. Interstitial brachytherapy was associated with external irradiation in 68 patients (group 1; mean dose, 48 Gy for external irradiation, 26 Gy for brachytherapy) or was exclusive in 26 patients (group 2; mean dose, 66 Gy). The mean follow-up was 44 months. Eleven acute complications were noted during or immediately after the implant (1 lethal myocardial infarction, 6 hematomas of the tongue which spontaneously resolved, 3 local sepsis). The mean duration of the mucositis was 9 weeks (from 4 to 20 weeks). Ten patients (17%) experienced a late complication (8 in group 1, 2 in group 2): 3 bone necroses requiring hemimandibulectomy (1 post-operative death), 1 tongue necrosis treated by a transoral mucosal excision, 6 bone expositions which recovered after medical treatment. Local control rates for T1 and T2 tumors were 75% (39/52) and 51% (21/41), respectively. Sixteen patients (17%) presented a nodal relapse which was associated in 6 cases with a concomitant local relapse. The local control rate of T1 tumors was 64% (23/36) in group 1 versus 100% (16/16) in group 2 (p < 0.01). For T2 tumors, these figures were 45% (14/31) and 70% (7/10), respectively (p > 0.3). The influence of 13 parameters on the local control was studied in analysis. In the one model analysis, a cox regression tumor size was significantly predictive of actuarial local recurrence (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)