Drug users' income-generating behaviours, such as prostitution, acquisitive crime and small-scale dealing, have a major influence on the harm caused to the non-using population. Using data on the drug use and income sources of 900 drug-injectors in Oslo, this paper has two aims: to present data on Oslo income-generating behaviours and compare these with those in the Netherlands and Scotland; and to explore conceptual issues in the comparison of self-reported dealing income with other sources. Eighty-three per cent of respondents reported income from social benefit, and 43% had sold drugs in the last month. Half the females reported income from prostitution. The income-generation differences found in the comparisons section do not seem to reflect variations in drug and other social policies, but may relate to differences in the profitability of dealing. Using self-reported dealing income to compare the contributions of different income sources may be misleading, however, since it does not reflect financial profit or the value of dealers' drug consumption. Adjusted figures show that theft accounts for 23% of total drugs expenditure, while the corresponding figures for dealing and prostitution are 42% and 21%, respectively.