Intrathecal baclofen (ITB) therapy can be very effective in the treatment of intractable spasticity, but its effectiveness and safety have not yet been thoroughly studied in children with cerebral palsy (CP). The aims of this double-blind, randomized, placebo-controlled, dose-finding study were to select children eligible for continuous ITB infusion, to assess the effective ITB bolus dose, and to evaluate the effects, side effects, and complications. Outcome measures included the original Ashworth scale and the Visual Analogue Scale for individually formulated problems. We studied nine females and eight males, aged between 7 and 16 years (mean age 13y 2mo [SD 2y 9mo]). Twelve children had spastic CP and five had spastic-dyskinetic CP. One child was classified on the Gross Motor Function Classification System at Level III, two at Level I V, and 14 at Level V. The test treatment worked successfully for all 17 children with an effective ITB bolus dose of 12.5[mu]g in one, 20[mu]g in another, 25[mu]g in 10, and 50[mu]g in five children. ITB significantly reduced muscle tone, diminished pain, and facilitated ease of care. The placebo did not have these effects. Nine side effects of ITB were registered, including slight lethargy in seven children. Fourteen children had symptoms of lowered cerebrospinal fluid pressure. We conclude that ITB bolus administration is effective and safe for carefully selected children with intractable spastic CP.