The effects of localized cooling/heating and injection/suction on the mixed convection flow on a thin vertical cylinder have been studied. The localized cooling/heating and (or) injection/suction introduce a finite discontinuity in the mathematical formulation of the problem which increases its complexity. In order to overcome this difficulty, a nonuniform distribution of wall temperature (heat flux) and surface mass transfer is considered at certain sections of the cylinder. The nonlinear coupled parabolic partial differential equations governing the mixed convection flow under boundary layer approximations have been solved numerically by using an implicit finite-difference scheme. The effects of the localized cooling/heating and (or) injection/suction on the heat transfer are found to be significant, but the effects of cooling/heating on the skin friction are comparatively small. The positive buoyancy force which assists the flow and the curvature parameter increase the skin friction and heat transfer. (C) 2003 Elsevier Ltd. All rights reserved.