The prevalence of "over-the-counter" monitors, was surveyed in infants referred to five Belgian paediatric centres between September 1987 and March 1988 for evaluation of their risk for sudden infant death (SID). Questionnaires were collected from 1625 families. Of the infants, 8.9% were already being monitored at home. For 78.1% of the infants no medical advice had been solicited, and for 21.9%, a paediatrician or a general practitioner had advised home monitoring without previous evaluation. Forty of 824 infants referred with no history of SID, and no history of apparent life-threatening event (ALTE), were monitored (4.8%). Monitoring was started for 3.8% (5 out of 130) of the infants who had lost a cousin or an uncle to SID, and for 22.2% (69 of 310) of the younger siblings of a SID victim. Of the 341 infants who had presented with an ALTE, monitoring was started in 32 (9.4%). The infants were monitored with respiratory monitors only, and in 86% of the monitors, the alarm delay had been regulated unnecessarily low.