The objective of the study was to determine the rate of uterine perforation associated with insertion of Multiload Cu375 in 'real-life' clinical use. It was a prospective observational cohort study using Prescription Event Monitoring methodology. There were 17,469 Multiload Cu375 insertions in 16,159 women between 1991 and 2001. The insertions were performed by 1,699 different doctors (mostly general practitioners) in surgeries, clinics, and hospitals throughout New Zealand. The results found 28 reports suggesting complete or partial uterine perforation, giving an incidence of 1.6 per 1000 insertions. Most perforations (86%) were not diagnosed at the time of insertion, with some remaining undiagnosed for several years. Doctors who reported inserting fewer than 10 Multiload Cu375 devices in the study period reported significantly more perforations than doctors who reported inserting between 10 and 100 devices did. In conclusion, we found the perforation rate in this study is higher than in clinical trials of Multiload Cu375. This might be because of inclusion of partial perforations in this study, a longer follow-up period, the large number of insertions studied, or because the majority of inserting doctors were less experienced than inserters in other studies.