Background <p>Despite evidence of variation in CYP3A5 expressor status between different ethnic groups, many transplant centres operate a ‘one size fits all’ immunosuppression policy in which all kidney transplant recipients receive the same weight-adjusted daily dose of tacrolimus, adjusted subsequently to achieve target blood concentrations.</p> Methods <p>We evaluated retrospective blood tacrolimus concentrations and tacrolimus doses in 382 patients based on self-described ethnicity.</p> Results <p>Median tacrolimus concentrations were lower in Black patients than those from other ethnic groups for the first four weeks following transplantation. More than 70% of measurements in Black patients were below target in the first and second weeks, and Black ethnicity was strongly associated with early subtherapeutic tacrolimus concentrations (odds ratio 3.49, <i>p</i> &lt; 0.001). There were no significant differences in transplant outcomes between ethnic groups, although the rate of acute rejection was higher in Black patients, despite greater use of anti-thymocyte globulin induction therapy in these patients.</p> Discussion <p>There is emerging evidence to support either prescribing based on CYP3A5 genotyping, or the empirical use of higher starting doses in Black patients. However, notwithstanding the complexities inherent in our understanding of ethnic identity, we advocate an approach where clinicians act proactively to avoid under-dosing in Black patients.</p> Clinical trial number <p>Not applicable. Bart’s Health NHS Trust audit number: 13,204.</p>