Several new chromosomal translocations resulting in driver fusion mutations have recently been discovered in non-small-cell lung cancer. The driver mutational patterns in pulmonary mucinous adenocarcinoma, a rare subtype of non-small-cell lung cancer, have not been well studied. A single-institute cohort study in Taiwan was performed to determine the mutations of epidermal growth factor receptor (EGFR), Kirsten rat sarcoma viral oncogene homolog (KRAS), fusions of anaplastic lymphoma kinase (ALK), c-ros oncogene 1 (ROS1), and neuregulin 1 (NRG1) in patients diagnosed with pulmonary mucinous adenocarcinoma. We also examined NRG1 translocation in patients diagnosed as adenocarcinoma of other subtypes with wild-type EGFR, KRAS, ALK, and ROS1 genes. Surgical or biopsy specimens were collected from 13 patients with mucinous adenocarcinoma. Using the direct RNA sequencing method, we discovered a rare CD74-NRG1 fusion (8 %), an echinoderm microtubule-associated protein like 4 (EML4)-ALK fusion (17 %), and three KRAS mutations (25 %). No EGFR mutations or ROS1 rearrangements were detected. The rare CD74-NRG1 fusion positive patient presented with uncommon radiological features. We did not detect any CD74-NRG1 fusion in the 109 adenocarcinoma of other subtypes, which were all negative for EGFR, KRAS, ALK, and ROS1. The CD74-NRG1 fusion mutation is rare and may be exclusively present in patients with pulmonary mucinous adenocarcinoma. Patients harboring CD74-NRG1 positive tumors may present with uncommon imaging features.