Checkout cashier work consists of handling a large number of items during a work shift, which implies repetitive movements of the shoulders, arms and hands/wrists, and a high work rate. The work is associated with a high prevalence of disorders in the neck and upper extremity. The concept of workstyle explains how ergonomic and psychosocial factors interact in the development of work-related upper extremity disorders. The aim of the project was to develop an instrument for the occupational health services to be used in the efforts to prevent upper extremity disorders in checkout cashier work. The instrument is based on the workstyle concept and is intended to be used as a tool to identify high-risk workstyle and needs for interventions, such as training and education. The instrument, BAsIK, consists of four parts; a questionnaire about workstyle, an observation protocol for work technique, a checklist about the design of the checkout and a questionnaire about work organization. The instrument was developed by selecting workstyle items developed for office work and adapting them to checkout cashier work, discussions with researchers and ergonomists, focus-group interviews with cashiers, observations of video recordings of cashiers, and studies of existing guidelines and checklists.