We explore whether and how auditor client portfolios evolve over auditor career stages. Using a ten-year panel data on Swedish auditors, we find that portfolio size grows in initial phases of the career but starts to decline when auditors have more than 13 to 18 years of experience (or are more than 46 to 54 years old). We also find that the frequency of having a listed client in the portfolio increases in the initial phases of the career stages and starts to decline in the later phases of the career. These results are consistent with the view that both experience and incentive factors shape auditors’ portfolios. Our cross-sectional test results show that auditors in the beginning of the career at Big 4 firms have fewer audit assignments than auditors at non-Big 4 firms, a result consistent with auditors at Big 4 firms having more time to develop their professional skills through work experience and coaching from more experienced auditors before taking on larger client portfolios. A final observation is that male auditors have larger client portfolios, more frequently listed clients and lower industry concentration of their portfolios. These results suggest that female auditors have portfolios that are less demanding to audit. A possible explanation is that female auditors are more risk-averse and place greater emphasis on having a client portfolio they are confident in being able to successfully audit. Overall, this study enhances our understanding of how careers develop at audit firms and how client portfolio characteristics evolve over auditors’ career stages in Big4 firms, large offices and male/female auditors.