To evaluate the role of needle diameter in causing postdural puncture headache (PDPH) in patients undergoingelective caesarian section. Study Design: Comparative cross-sectional study. Place and Duration of Study: This study was conducted inDepartment of Anaesthesia and Intensive care PNS Shifa Karachi over duration of six months. Patients and Methods: It was a cross sectionalstudy of 100 patients, which were divided into two separate groups. Group I and Group II were given spinal anaesthesia with 25 gauge and 27gauge Quincke needles respectively. In both the groups the patients were randomly selected and were blind to size of the spinal needle used.Results: The data was analyzed using Chi-square test. A P value of <0.05 was considered statistically significant. Two patients in 25-G groupand one in 27-G group required additional general anaesthesia because of inadequate spinal anaesthesia. Thus, a total of three patients wereexcluded from the study. Five out of forty-eight patients in group 1 and one out of forty-nine patients in Group II suffered from post spinalheadache. Conclusions: The proportion of patients with post spinal headache with 25 G needle is significantly more than those with 27 G.