This book constitutes the refereed proceedings of the 9th International MICCAI Brain Lesion Workshop, BrainLes 2023, as well as the Stroke Workshop on Imaging and Treatment Challenges, SWITCH 2023. These events were held in conjunction with the Medical Image Computing for Computer Assisted Intervention Conference, MICCAI 2023, during October 8-12, 2023.

The 15 revised full papers presented in this volume were selected form 23 submissions. They describe the research of computational scientists and clinical researchers working on brain lesions, and specifically glioma, multiple sclerosis, cerebral stroke, traumatic brain injuries, vestibular schwannoma, and white matter hyper-intensities of presumed vascular origin.