Background Next-generation sequencing is available for assessing genomic alterations in non–small-cell lung cancer (NSCLC), although the performance characteristics and clinical utility has not been well characterized. This technique can be used to sequence hundreds of known cancer-associated genes. Our aim was to investigate the diagnostic success and clinically relevant results of extensive sequencing in NSCLC patients. Patients and Methods A case series of 49 NSCLC patients was used to determine the success of extended next-generation sequencing, record genomic alterations, and evaluate clinical utility. Data were collected in a retrospective review. Sequencing was performed using a hybridization capture of 3320 exons from 236 cancer-related genes and 47 introns of 19 genes applied to ≥50 ng of DNA and sequenced to high, uniform coverage of 622 times. Results Sequencing was successful in 29 of 32 (91%) surgical/excisional specimens, and 12 of 17 (71%) nonsurgical specimens including an endoscopic forceps biopsy, core needle biopsies, fine-needle aspirates, and effusion cytologies. All 5 transthoracic core needle biopsies failed. A total of 179 genomic alterations (average 4.37 per tumor) were found. A total of 63 were clinically relevant (average 1.54 per tumor). The most frequently mutated genes were tumor protein p53, cyclin-dependent kinase inhibitor 2A, megalencephalic leukoencephalopathy with subcortical cysts 1, rapamycin-insensitive companion of mammalian target of rapamycin, epithelial growth factor receptor, SWI/SNF Related, Matrix Associated, Actin Dependent Regulator Of Chromatin, Subfamily A, Member 4, cyclin-dependent kinase inhibitor 2B, phosphatidylinositol-4,5-bisphosphate 3-kinase, catalytic subunit α, Kirsten rat sarcoma viral oncogene homolog, Erb-B2 receptor tyrosine kinase 2, Serine/Threonine Kinase 11, and NK2 Homeobox 1. Sequencing results led to a change in management in 7 of 49 cases (14.3%). Conclusion Extended next-generation sequencing was performed successfully in 41 (83.7%) cases of NSCLC using a range of pathology specimens. Testing had the potential to affect treatment decisions in selected patients.