Tinnitus can cause extreme morbidity. Despite many attempts to find a treatment for idiopathic cases, they remain difficult to manage. Because nerve injury is one of the suspected etiologies of tinnitus and because gabapentin has been found to be effective in treating nerve injuries, some authors have attempted to determine if gabapentin has a role in treating tinnitus. Although gabapentin was found to be ineffective for tinnitus in these previous studies, to the best of our knowledge no studies have been performed that took into consideration the presence of various accompanying factors and concomitant diseases that might influence its effect. We conducted a prospective, randomized, double-blind, placebo-controlled clinical trial of gabapentin for idiopathic tinnitus. We treated 40 patients with gabapentin and measured its effectiveness by comparing differences between pre- and post-treatment Tinnitus Severity Index (TSI) values and tinnitus loudness scores. We also compared these outcomes with those of a group of 40 matched placebo controls. At study's end, we found no significant differences between the gabapentin and control groups in mean decreases in TSI value and loudness score (p = 0.85 and p = 0.12, respectively). However, we did find that patients with hypertension, diabetes, and/or dyslipidemia showed a better response to gabapentin than did those with tinnitus alone (p = 0.01). We conclude that although there was no statistically significant difference between gabapentin and placebo in treating isolated tinnitus or tinnitus overall, patients with concomitant hypertension, diabetes, and/or dyslipidemia may benefit from gabapentin.