Pruritus is a common adverse effect of opioids, particularly after spinal and epidural administration. Although not harmful in itself, pruritus can be troublesome and affect patients' quality of life and motivation to continue opioid treatment. Several mechanisms have been postulated, but the pathogenesis of opioid-induced pruritus is still not fully understood. The µ-opioid receptor system seems to play a central role. Many treatment strategies have been tried in the management of opioid-induced pruritus, but none have proven to be completely satisfactory. Treatment with the µ-opioid receptor antagonist naloxone or the serotonin 5-HT(3) receptor antagonist ondansetron has documented effect.