Objectives To compare the frequency of headache and the procedure time following lumbar puncture (LP) using a 25-gauge needle compared to a 22-gauge needle.

Design 4-period crossover blinded randomised controlled trial.

Setting Oncology unit, Royal Children's Hospital, Melbourne.

Patients Children aged 4–15 years at enrolment having LPs as part of their treatment for leukaemia.

Interventions Each child was allocated a random sequence of four LPs, two with a 22-gauge and two with a 25-gauge needle.

Outcome measures The presence of post-LP headache. Secondary outcomes included the presence of any headache, procedure time and impact of headache on the family.

Results Data on 341 procedures in 93 randomised children were analysed. There was little difference in the incidence of post-LP headache between the two needle sizes (22-gauge 7.2%, 95% CI 3.8 to 12.2; 25-gauge 4.6%, 95% CI 2.0 to 8.9, p=0.3) or in the incidence of any headache (22-gauge 18% 95% CI 12.5 to 24.6; 25-gauge 15%, 95% CI 10.0 to 21.1, p=0.4). Use of the 25-gauge needle was associated with longer procedure times. The incidence of post-LP headache showed little evidence of an age effect (OR =1.1, 95% CI 0.98 to 1.3) and was higher in girls than in boys (11% vs 3%, respectively, OR=3.3, 95% CI 1.3 to 8.4, p=0.014). Fifty-five per cent of families with a child with a post-LP headache assessed the overall functional impact as moderate or severe.

Conclusions There was little difference in the occurrence of post-LP headache or any headache between procedures carried out using the 22-gauge or 25-gauge needles. Depending on the circumstances of the procedure and the experience of the operator, either gauge may be appropriate for an LP in a child.