The purpose of this study is to compare the effect of bed rest on the post lumbar puncture headache in pediatric oncologic patients, to analyse the risk factors of post lumbar puncture headache, and to speculate objective rationale for the management of patient undergone lumbar puncture. In this prospective case-control study, for the 3 month period, from January 3, 1996 to March 30, 1996, the in-patients admitted to the S National University Hospital pediatric ward for chemotherapy were enrolled, and were randomly assigned to the groups, of 1 hour or of 6 hours post lumbar puncture bed rest One hundred and thirty two lumbar puncture was studied and 66 case assigned to 1 hour group, and 66 case to 6 hours group. The response of the patient was assessed by McGrath's Face Scale and Oucher Pain Scale for patient less than 7 years of age, and by Verbal Rating Scale and Visual Analog Scale for patient great equal than 7 years of age. The medical records were reviewed and two nurses, whose career is more than 3 years in pediatric unit, interviewed the patients or parents with formulated questionnare, and the collected data was analyzed by Chi-square test, Student t-test and Ridit analysis, using PC-SAS statistic package. In the study population, the mean age was 8.8 years and the male proportion is slightly larger than female (67.4%). The most common diagnosis was acute lymphocytic leukemia (62.1%), and malignant lymphoma, acute myelogenous leukemia, retinoblastoma, rhabdo-myosarcoma, and neuroblastoma were involved, in such order. The incidence of post lumbar puncture headache was 16.7%, and no significant difference in the incidence according to age(t=-0.248, P=0.804) or sex(x²=0.835, P=0.361). The study was proved that the incidence of post lumbar puncture headache is not influenced by WBC count, previous tapping, drained amount of cerebrospinal fluid, previous headache, skill of the doctor, gauge of the needle, attempt to puncture, sedation, and bone marrow examination. The incidence of post lumbar puncture headache in acute lymphocytic leukemia was 18.3%, and 22.2%, 0%, 11.1%, 14.3% and 50% in malignant lymphoma, acute myelogenous leukemia, retinoblastoma, rhabdomyosarcoma and neuroblastoma, respectively. The severity of headache, and the incidence of nausea, vomiting, and lumbago was not influences by the diagnosis The incidence of headache was not influenced by the duration of post lumbar puncture bed rest, and the incidence of headache was 10.6% and 22.7% in 1 hour group and 6 hour group, respectively. The severity of headache, nausea, vomiting, and lumbago was not also differ in both group. With such results, at least, the suggestion that in pediatric patient, more than 6 hours post lumbar puncture bed rest is no more obligate management for prevention of headache, was speculated