A permanent magnet rotor for an brushless electric motor of the kind having an internal stator, has a supporting structure made of molded plastic that includes an essentially disc-shaped portion to which a shaft is centrally connected. The periphery of the disc is joined to an essentially cylindrical cage portion which extends coaxially around the shaft. A plurality of magnetically conductive yokes are disposed in the cage portion. The yokes are shaped as ring segments which as a whole form an essentially cylindrical wall. A plurality of ring segment permanent magnets are each disposed astride the junction of a pair of adjacent yokes. Each yoke has a dimension which increases from the circumferential ends thereof towards its circumferentially intermediate portion, such that the cross-sectional area of the yoke in a radial plane correspondingly increases from the ends thereof towards its intermediate portion.