Purpose <p>To examine the associations between shift or night work and irregular periods and period pain among two cohorts of Australian women, using data collected 16 years apart.</p> Methods <p>We used data from the 1989–95 (<i>n</i> = 6,767) and 1973–78 (<i>n</i> = 7,527) cohorts from the Australian Longitudinal Study on Women’s Health, when participants were aged 24–30 years. Logistic regression models were used to assess the association between night or shift work and severe period pain and irregular periods, and to compare them to non-shift or night workers.</p> Results <p>Women from the 1989–95 cohort who did night work reported higher odds of having experienced irregular periods (AOR = 1.28, 95% CI: 1.03, 1.59) compared to those who undertook shift work. However, there was no association between night work and severe period pain (AOR = 1.10, 95% CI: 0.86, 1.41). Among women in the 1973–78 cohort, neither severe period pain (AOR = 1.20, 95% CI: 0.82, 1.76) nor irregular periods (AOR = 1.38, 95% CI: 0.92, 2.06) were associated with night work. Across both cohorts, no associations were found between shift or night work and irregular or severe period pain when comparing shift or night workers combined to non-shift or night workers.</p> Conclusions <p>Night workers reported higher odds of irregular periods compared to shift workers in the 1989-95 cohort; however, no consistent association was found with severe period pain. Future research should investigate whether this association is causal. Supportive workplace practices may benefit night workers experiencing irregular periods.</p>