Abstract: Flexible automatic assembly is an emerging need in several industries in the developed countries, owing to the growing market request of small batch productions. This paper introduces a new class of flexible assembly systems, that we define as fully-flexible assembly systems (F-FAS), and addresses the problem of comparing their direct production costs to that of a generic flexible robotized work cell, whose reconfiguration for batch change requires time. Conversely, the F-FAS is a fully-flexible system, able to handle a highly mixed production order in which the size of the batch may be as small as one piece. Convenience analysis revealed that the F-FAS becomes more convenient in certain conditions, especially with complex assemblies and small batch sizes. First experimental data are presented to demonstrate the viability of the fully-flexible system.