Objectives Survivors of diffuse large B-cell lymphoma (DLBCL) are at an increased risk of developing second primary malignancies. However, the risk of secondary acute myeloid leukaemia (sAML) has not been previously described in detail, and the outcomes of patients with sAML are also undiscovered compared with their de novo counterparts (de novo acute myeloid leukaemia, dnAML). Design This study is a retrospective database study. Setting and participants A total of 70 280 patients with primary DLBCL, diagnosed between 2000 and 2016, were identified from the Surveillance, Epidemiology, and End Results (SEER) database. Another cohort with dnAML matching with sAML was also obtained from SEER database. Results The standardised incidence ratio was 6.23 (95% CI: 5.50 to 7.03) for sAML among survivors of DLBCL. The estimated cumulative incidence of sAML was 0.61% 15 years after the diagnosis of DLBCL. Patients aged 60-74 years were more likely to have sAML than those <60 years (subdistribution HR (sHR)=1.417; 95% CI: 1.087 to 1.850), whereas patients aged >= 75 years were less likely to have sAML (sHR=0.648; 95% CI: 0.452 to 0.930). Patients with advanced-stage DLBCL were more prone to sAML than those with early-stage disease (sHR=1.307; 95% CI: 1.012 to 1.690). There was a significant difference of survival between patients with dnAML and those with sAML (HR=1.25; 95% CI: 1.01 to 1.53). Conclusions The risk of developing sAML after DLBCL is substantial. Patients aged 60-74 years and with advanced-stage are more prone to sAML. And, compared with their dnAML counterparts, patients with sAML have a worse prognosis.