The reliability of suicide reporting remains a concern. Problems include procedural deficiencies, ambiguous evidence and the determination of intent. In this study, Queensland Suicide Register (QSR) data were compared to the usual official source - the Australian Bureau of Statistics (ABS). QSR deaths were coded as beyond reasonable doubt, probable and possible. These categories were analysed by methods and demographic variables to determine the nature of difficult-to-classify suicides. QSR suicides exceeded ABS especially for females, ages 25-44, and the methods overdose, drowning and 'other methods'. Opiate overdoses were most difficult to code. Ambiguous circumstantial information and unclear intent were major impediments. Nations witnessing rising rates of deaths due to drug abuse need to monitor undetermined and accidental deaths as well as suicides.