Māori have been overrepresented in the New Zealand criminal justice system for decades. Māori are significantly more likely to be disadvantaged by risk factors which are linked to criminal offending behaviours. Overseas research suggests that there may be a bias from officials against minority groups within criminal justice systems around the world, in which minorities are more likely to be arrested or receive harsher sentences given equivalent behaviour. However, limited research on this issue has been conducted in New Zealand. The current study updates Fergusson, Horwood and Lynskey (1993) who found that Māori/Pacific Island children were 2.9 times more likely than Pākehā children to come to the attention of the Police. The present study used the same longitudinal sample as the 1993 study, followed from adolescence through to age 35 (N = 995). The present study examined the associations between rates of offending and ethnicity (Māori versus non-Māori) both before and after controlling for disadvantageous social, family and individual risk factors which have previously been linked to offending behaviours. Specifically, the study investigated whether there is any evidence of an ethnic bias against Māori within the criminal justice system after controlling for these factors. Generalised estimating equation (GEE) models were fitted to repeated measures data to examine the strength of the associations between Māori ethnicity and rates of offending. The GEE models were then extended in a series of adjustments to control for social, family and individual risk factors, and again to include self-reported rates of violent, property and other offences. Results found that Māori offend at a significantly higher rate compared to non-Māori, and that even when known risk factors of offending and self-reported rates of offending were controlled for, a small residual bias was evident. Although results were not statistically significant after adjusting for risk factors, the consistency of the results (with several different measures showing similar trends) suggests that there may be an ethnic bias against Māori within the criminal justice system. These findings may aid in addressing the issue of Māori being overrepresented and consequently reduce the number of Māori in the New Zealand criminal justice system.