Direct Methanol Fuel Cells (DMFCs) have recently attracted the interest of portable applications due to their superior specific energy density compared to the best rechargeable battery and for their potentialities of instantaneous refueling. The most recent literature in the field of DMFCs has directed increasing interest on the role of the flow fields on the performance of the FC itself. The most "primitive" designs (e.g. parallel channels) have generally been dismissed and substituted by serpentine or interdigitated flow patterns. The serpentine pattern forces the entire feed flow rate to pass through a serpentine spanning over the entire electrode surface. This system is particularly suited to drive gas bubbles out of the system and therefore it seems to be particularly suited for the methanol side. The interdigitated flow field pattern is particularly suitable only for the air feed to the DMFC. The effect of the channel and graphite rib geometries is of critical importance. The choice of the correct geometry is thus a question of compromise which can be drawn on the grounds of modeling calculations and experimental checks. A series of simulations in CFD (fluent 6.1) were thus performed on a multichannel serpentine matrix for the anode side (methanol feed) piled up in a stack hosting 40 MEAs (nominal power 250 W; 222 cm2 membrane surface per cell). Three different channel geometries were modeled. This paper shows that a series flow is not suitable for the too high pressure drop and average velocity into channels it implies. Optimal flow distribution (i.e. low pressure drop, acceptable average velocity and a good methanol distribution) seems to be guaranteed with three serpentines per cell for fuel cell stacks of a nominal power of 250 W.