Background <p>Sarcoidosis is a systemic granulomatous disease, often affecting the lungs, with a generally favourable prognosis. However, some patients experience progressive disease, and cardiac involvement may worsen outcomes. Data on the clinical course and causes of death in pulmonary sarcoidosis (PS), particularly with coexisting cardiac sarcoidosis (CS), remain limited.</p> Methods <p>We retrospectively analysed patients with histologically confirmed PS. Baseline evaluations included chest X-ray and computed tomography, pulmonary function tests, and echocardiography. CS was diagnosed based on the findings of ¹⁸F-fluorodeoxyglucose positron emission tomography and cardiac magnetic resonance imaging in patients who met the predefined clinical screening criteria.</p> Results <p>A total of 513 patients met the study criteria. The 3-, 5-, and 10-year survival rates were 98.2%, 97.0%, and 94.6%, respectively (median follow-up: 6.7 years). CS was diagnosed in 48 patients (9.4%), and survival was poorer in those with CS (<i>p</i> = 0.004 by log rank test). Multivariate analysis showed that CS was associated with increased all-cause mortality after adjustment for age or sex (age-adjusted hazard ratio 3.55, 95% CI 1.18–10.6; sex-adjusted hazard ratio 3.79, 95% CI 1.28–11.2). During follow-up, 21 patients (4.6%) died. Malignancy was the leading cause of death (<i>n</i> = 10, 48%), followed by cardiac death (<i>n</i> = 3, 14%) and respiratory failure (<i>n</i> = 3, 14%).</p> Conclusions <p>In this Japanese single-centre cohort of patients with predominantly mild histologically confirmed PS, CS identified through a screening-based diagnostic pathway was associated with increased all-cause mortality.</p>