Serotype 3 pneumococcal infection can cause severe invasive disease, even in immunocompetent adults, and is potentially preventable by vaccination. Invasive pneumococcal disease caused by serotype 3 is currently the most frequent serotype found in adults in Denmark. In this report, we present a 62-year-old immunocompetent man diagnosed with a severe pleural empyema caused by serotype 3, requiring a long course of antibiotics. The patient experienced clinical improvement, and follow-up imaging showed near-complete resolution of lung infiltrates. We also review the epidemiology of serotype 3 invasive pneumococcal disease in adults in Denmark and discuss the challenges related to serotype 3 and effective vaccines.