The first approach towards the automatic layout generation of resonant-type metamaterial transmission lines by using space mapping optimisation is reported. Specifically, the so-called aggressive space mapping (ASM) technique is applied for synthesising microstrip lines loaded with complementary split ring resonators (CSRRs). From a certain set of elements of the circuit model of the unit cell of such lines (which is typically derived from system specifications), the topology (layout) of the CSRR-loaded microstrip line, providing the same electromagnetic response as the circuit model (within certain error limits), is generated automatically. This synthesis technique is of paramount importance for the design of metamaterial-based (or inspired) circuits implemented by means of electrically small resonators such as CSRRs and SRRs. Although the reported technique is applied here to the synthesis of a negative permittivity structure (CSRR-loaded line), the basics towards the extension of the technique to other artificial transmission lines are clearly established. © 2010 The Institution of Engineering and Technology.