To assess the role of comorbidity on outcome in elderly patients with glioblastoma treated with radiotherapy plus concomitant and adjuvant Temozolomide, patients over 65 years with glioblastoma, who underwent surgical resection or biopsy and radiochemotherapy, were evaluated. The Adjusted-Age Charlson Comorbidity Index and the Adult Comorbidity Evaluation-27 were used to assess comorbidity. From April 2005 to January 2011, 35 patients (median age 72 years) were treated in our Institution. Thirteen patients had a Charlson score more than 3, while, according to the Adult Comorbidity Evaluation-27, 21 patients had mild or severe comorbid conditions. Patients with low Charlson comorbidity score experienced a longer survival time than those with higher score (22 vs. 10 months, respectively). The Adjusted-Age Charlson Comorbidity Index influenced survival at univariate and multivariate analysis (p = 0.004, p = 0.001, respectively). No comorbidity index was a predictor for progression-free survival. Our data suggested that the association of radiotherapy with TMZ was safe and effective. Perhaps, the comorbidity assessment could be an appropriate tool in the treatment decision for elderly patients with glioblastoma.