Introduction <p>A large number of middle-aged and elderly patients have an insufficient understanding of osteoporosis and its harm. This study aimed to establish and validate a convolutional neural network (CNN) model based on unenhanced chest computed tomography (CT) images of the vertebral body and skeletal muscle for opportunistic screening in patients with osteoporosis.</p> Materials and methods <p>Our team retrospectively collected clinical information from participants who underwent unenhanced chest CT and dual-energy X-ray absorptiometry (DXA) examinations between January 1, 2022, and December 31, 2022, at four hospitals. These participants were divided into a training set (<i>n</i> = 581), an external test set 1 (<i>n</i> = 229), an external test set 2 (<i>n</i> = 198) and an external test set 3 (<i>n</i> = 118). Five CNN models were constructed based on chest CT images to screen patients with osteoporosis and compared with the SMI model to predict the performance of osteoporosis patients.</p> Results <p>All CNN models have good performance in predicting osteoporosis patients. The average F1 score of Densenet121 in the three external test sets was 0.865. The area under the curve (AUC) of Desenet121 in external test set 1, external test set 2, and external test set 3 were 0.827, 0.859, and 0.865, respectively. Furthermore, the Densenet121 model demonstrated a notably superior performance compared to the SMI model in predicting osteoporosis patients.</p> Conclusions <p>The CNN model based on unenhanced chest CT vertebral and skeletal muscle images can opportunistically screen patients with osteoporosis. Clinicians can use the CNN model to intervene in patients with osteoporosis and promptly avoid fragility fractures.</p> Critical relevance statement <p>The CNN model based on unenhanced chest CT vertebral and skeletal muscle images can opportunistically screen patients with osteoporosis. Clinicians can use the CNN model to intervene in patients with osteoporosis and promptly avoid fragility fractures.</p> Key Points <p><UnorderedList Mark="Bullet"> <ItemContent> <p>The application of unenhanced chest CT is increasing.</p> </ItemContent> <ItemContent> <p>Most people do not consciously use DXA to screen themselves for osteoporosis.</p> </ItemContent> <ItemContent> <p>A deep learning model was constructed based on CT images from four institutions.</p> </ItemContent> </UnorderedList></p> Graphical Abstract <p></p>