Credit unions in Northern Ireland are subject to a unique combination of statutory oversight and self-regulation. This paper investigates the association between prudence and the monitoring of financial ratios by credit union trade associations. We find that compliance with the mandated level of capital reserves is uniformly high, regardless of the existence or extent of self-regulation. However, after controlling for cross-sectional differences in profitability, age, size, growth and common bond type a positive association exists between self-regulation and financial ratios measuring prudence and loan book quality. These findings have policy implications for the regulation of credit unions in Northern Ireland and elsewhere regarding potential regulatory cost savings from reliance on self-regulation provided by trade associations.