BACKGROUND: Intrathecal adjuvants has gained popularity with the aim of prolonging the duration of block, quality of block and decreased resource utilization compared with general anaesthesia. The purpose of this study was to evaluate the optimum dose, onset and duration of sensory and motor block as well as adverse effects of adding Dexmedetomidine to hyperbaric bupivacaine for spinal anesthesia. DESIGN: randomized double blind trail. SETTING: hospital based study. METHOD: 90 Patients between the period of January to June 2013 were randomly allocated to three groups of 30 each to receive intrathecally either 15 mg hyperbaric bupivacaine alone (group B) or 10 µg (group D10), 5µg (group D5) of dexmedetomidine added to 15 mg hyperbaric bupivacaine. The onset time to reach T10 sensory and Bromage 3 motor level, the regression time for S1 sensory and Bromage 0 motor block, Sedation scores, hemodynamic changes and side effects were recorded. STATISTICAL ANALYSIS: Performed using computer statistical software system SPSS version 16. Data were expressed as either mean and standard deviation or numbers and percentages. Continuous covariates (age, height, weight and duration of surgery) were compared using analysis of variance (ANOVA). For categorical covariates (gender, ASA class, blood transfusion, nausea/vomiting, hypotension, bradycardia, use of ephedrine, additive analgesia, atropine and type of surgery) a Chi-square test was used, with the p value reported at the 95% confidence interval. For the time to reach T10 dermatome, Bromage 3 scale, and the regression of the sensory block to S1 dermatome and Bromage scale 0, ANOVA test was used to compare the means. The level of significance used was p<0.05. The total sample size was calculated to be 90 (30 patients in each group). RESULTS: Onset of bromage 3 motor block and time to reach T10 sensory dermatome level was statistically significant between group B and group D5, D10 (P <0.05, B vs D5,D10). The time for regression of sensory block to S1 dermatome and bromage 0 motor blocks was increased by addition of dexmedetomidine in a dose dependent manner. (p <0.001, B vsD5, D10. D5vsD10). CONCLUSION: There is a dose dependent prolongation of sensory and motor block regression time with the addition of Dexmedetomidine up to 10 µg as an adjuvant without any significant increase in the side effects.