Stroke events are being registered in 27 of the MONICA collaborating centres. Coding of test cases has shown the greatest discrepancies in coding of the type of stroke (different pathoanatomical diagnoses) and of the diagnostic category (whether a definite stroke has occurred or not), 23% and 14% discrepancies respectively. A check for completeness of stroke registration at the Northern Sweden MONICA Center showed that more than 91% of the events were retrieved by routine registration procedures. Measures to reduce the discrepancies in coding between centres and to check for completeness of data are suggested. In many centres, the number of stroke events below 65 years of age is too small to permit meaningful analyses. By including also stroke events in the 65-74 year age range, the number of fatal events in the Northern Sweden MONICA area increased by 195% and non-fatal events by 149%. Many other MONICA centres have also extended their upper age limit for the registration of stroke events, thus improving the preconditions for statistical evaluations of the long-term changes in stroke incidence.