A sample of 329 heroin users were interviewed about their experiences at other peoples' heroin overdoses. The overwhelming majority (86%) had witnessed a heroin overdose, on a median of six occasions. Heroin users were reluctant to seek medical attention, with an ambulance being called on only half (56%) of the most recent overdose occasions. At only 17% of most recent overdoses was calling an ambulance the first action taken. Males reported taking significantly longer than females to call an ambulance. Nearly half (44%) of subjects reported that there were factors that had delayed or stopped them seeking medical assistance, the most common impediment being a fear of police involvement. The importance of interventions to encourage help-seeking at overdoses are discussed.