Mass customisation increases the number of product variants, shortens product cycles, and results in increasingly complex production systems. The complexity needs to be defined, and further operationalized to support management of production complexity. This paper's contribution is the empirical findings of perceived production complexity at three manufacturing companies, from the perspective of different functions/roles within the production systems; production engineers, operative personnel, internal logistics, and in one company also man-hour planning. Data was collected through observations, interviews, and cross-functional workshops. Results show that mass customisation is the greatest driver and cause of complexity. The increase of product variants affects complexity for all three investigated roles in the production system.