In this paper, we introduce a new assembly line balancing problem in which tasks differ with respect to their qualification requirements and the qualification levels of workers are ranked hierarchically. In the hierarchical workforce structure, a lower qualified worker can be substituted by higher qualified ones with a higher cost. The resulting problem is referred to as assembly line balancing with hierarchical worker assignment (ALB1-11N). The ALBHW problem consists in finding the optimal assignment of workers and tasks to the stations such that total cost is minimized. We have formulated an integer linear programming model to solve this problem. The computational results are obtained and analyzed on a large number of ALBHW instances. (C) 2014 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.