Side effects of iohexol myelography are known to largely depend on the leakage amount of cerebrospinal fluid at the puncture site of the dura. To evaluate the relationship between side effect incidence and spinal needle size and to assess the possibility of performing myelogrphy in outpatients, iohexol myelography was performed in 100 patients (58 inpatients and 42 outpatients) using variable sized needles. A questionaire including presence or absence, duration and degree of various side effects was used for evaluation of side effects. The overall side effects included headache(15%), back pain (14%), dizziness(9%), and nausea (4%), etc. The incidences of side effects were 28.0% in total, and 16.7%, 23.5%, 26.3%, 46.4% in patients using 25G, 23G, 22G, 21G spinal needles, retrospectively. The difference of side effect incidence was not significant between male and female. In conclusion, the use of fine spinal needles (25-26G) is recommended to decrease the side effect incidences in myelgraphy. Our findings support the use of fine needle myelography as a safe, less side-effect procedure, not only for in patients but also for out patients.