2035 Background: We compared two different schedules of temozolomide (TMZ) concomitant therapy in terms of toxicity and outcome. Methods: 70 patients (median age 61 years, range 27–80) affected by high grade gliomas were treated with concomitant chemoradiation. Conformal radiotherapy (5,940 cGy, 180 cGy/day; CTV2: tumor bed + residual tumor if present + oedema, 3,960 cGy; CTV1: tumor bed + residual tumor if present + margins, 1,980 cGy) was associated with one of the following TMZ schedules: TMZ1: (75 mg/m2 × 5 days, first and last week of radiotherapy); TMZ2 (75 mg/m2, 7 days/week, from the first to the last day of radiotherapy); Toxicities were graded according to RTOG criteria. Survival analysis based on the Kaplan-Meier model. Results: From October, 2000 to March, 2006, 54 patients high grade gliomas were evaluated. 41 patients (29 GBL, 70.7%; 12 AA, 29.3%) were treated between October 2003 and March 2006 with TMZ2, and compared to an historical series of 29 patients (25 GBL, 86.2%; 4 AA, 13.%) treated in our Institution before 2003 with TMZ1. All patients received adjuvant chemotherapy with TMZ for 6 cycles or until disease progression. Hematological toxicity was mild in both group, whereas neurological toxicity (seizures) was higher in TMZ2 group, with a grade > 2 toxicity registered in 11/41 pts (26.8%) compared to 1/29 of the TMZ1 group (3.5%), even if this difference failed to achieve statistical significance (p=0.06). The overall survival did not significantly differ among the 2 schedules (p=0.60). In fact, at a median follow-up of 21 months (range 3- 68), median survival time was 21 months and 19 months, for TMZ1 and TMZ2 groups, respectively, with a 1-year and 2-year overall survival of 73.1% in the TMZ1 group and 75.3% in the TMZ2 group, respectively. Conclusions: In our experience, the concomitant administration of TMZ at the daily dose of 75 mg/m2 given continuously or only in the first and the last week of radiotherapy obtained comparable results in terms of outcome, with a heavier neurological toxicity when given 7 days per week, from the first to the last day of radiotherapy. These data suggest that, in selected cases, the TMZ1 schedule can be considered as a safe, alternative strategy, which does not impact significantly on patient outcome, compared to the standard TMZ2. No significant financial relationships to disclose.