Aims This study aimed to evaluate the outcome and prognostic factors in patients with dilated cardiomyopathy (DCM) and long‐standing heart failure (LDCM) vs. recent‐onset heart failure (RODCM). Methods and results We compared 2019 patients with RODCM (duration <6 months, mean age 58.6 years, 70.7% male) with 1714 patients with LDCM (duration ≥6 months, median duration 3.5 years, mean age 62.5 years, 73.7% male) included in the Swedish Heart Failure Registry in the years 2003–16. Outcome measures were all‐cause, cardiovascular (CV), and non‐CV death and hospitalizations; heart transplantation; and a combined outcome of all‐cause death, heart transplantation, or heart failure (HF) hospitalization. Multivariable risk factor analyses were performed for the combined endpoint. All outcomes were more frequent in LDCM than in RODCM. The multivariable‐adjusted hazard ratios (HRs) (95% confidence interval) for LDCM vs. RODCM were 1.56 (1.34–1.82), P < 0.0001, for all‐cause death over a median follow‐up of 4.2 and 5.0 years, respectively; 1.67 (1.36–2.05), P < 0.0001, for CV death; 2.12 (1.14–3.91), P < 0.0001, for heart transplantation; 1.36 (1.21–1.53), P < 0.0001, for HF hospitalization; and 1.37 (1.24–1.52), P < 0.0001, for the combined outcome. A propensity score‐matched analysis yielded similar results. CV death was the main cause of mortality in LDCM and was higher in LDCM than in RODCM (P < 0.0001). Almost all co‐morbidities were significantly more frequent in LDCM than in RODCM, and the mean number of co‐morbidities increased significantly with increased duration of disease, also after age adjustment. Age, New York Heart Association functional class, ejection fraction, and left bundle branch block were prognostically adverse. The only co‐morbidity associated with the combined outcome regardless of HF duration was diabetes, in LDCM HR 1.34 (1.15–1.56), P = 0.0002 and in RODCM HR 1.29 (1.04–1.59), P = 0.018. Male sex HR 1.38 (1.18–1.63), P < 0.0001 and aspirin use HR 1.33 (1.14–1.55), P = 0.0004 carried increased risk only in RODCM. Heart rate ≥75 b.p.m. HR 1.20 (1.04–1.37), P = 0.01, atrial fibrillation HR 1.24 (1.08–1.42), P = 0.0024, musculoskeletal or connective tissue disorder HR 1.36 (1.13–1.63), P = 0.0014, and diuretic therapy HR 1.40 (1.17–1.67), P = 0.0002 were prognostically adverse only in LDCM. Conclusions This nationwide study of patients with DCM demonstrates that longer disease duration is associated with worse prognosis. Co‐morbidities are more common in long‐standing HF than in recent‐onset HF and are associated with worse outcome. With the increased survival seen in the last decades, our results highlight the importance of careful attention to co‐morbid conditions in patients with DCM.