Download https://doi.org/10.1016/j.jmsy.2013.04.011 Modern assembly systems are adapting to the increased mass customization resulting in shorter cycle times, more variants and increased complexity for final assembly operators. More variants require additional support functions targeted for assembly operators to avoid assembly errors. This paper investigates four relations between Choice complexity, Cognitive Automation and Assembly errors. Assembly errors were measured from historical data and cognitive automation was assessed on a task level. Results show that complexity positively correlates with assembly errors and that the usage of cognitive support is low. Over 60% of all tasks in the study were performed based on own experience. Increased usage of cognitive automation is needed in final assembly to minimize the negative effects of complexity.