The SLOSH-MRI (Swedish Longitudinal Occupational Survey of Health – Magnetic Resonance Imaging) project is an ongoing population-based neuroimaging study initiated in 2021. More than 500 participants aged 50–70 years have been recruited from the Swedish Longitudinal Occupational Survey of Health (SLOSH). The present NAISS project will analyse multimodal MRI and related data from approximately 395 participants with available data relevant to the planned analyses. SLOSH is a longitudinal cohort originally drawn from nationally representative samples of the Swedish working population and provides extensive longitudinal information on work, health, lifestyle, psychosocial factors, sleep and ageing. SLOSH-MRI extends this resource with detailed neuroimaging, physiological, cognitive and biological measures, enabling investigation of the relationships between psychosocial factors, physical health, cognition and brain ageing. The available data include sociodemographic, psychosocial and lifestyle measures; work-related and perceived stress; self-reported and objectively measured sleep; vascular and metabolic risk factors; physical function and cardiorespiratory-fitness measures; cognitive assessments; and stress-related, inflammatory and vascular biomarkers. Neuroimaging measures comprise structural T1-weighted MRI, FLAIR, resting-state fMRI, task fMRI, quantitative susceptibility mapping (QSM), and diffusion MRI (dMRI). The NAISS allocation will support secure storage and processing, quality control, preprocessing and statistical analysis of these multimodal imaging data and their integration with relevant SLOSH-MRI measures.