Boundary layer transition is significant to many flow fields that include both laminar and turbulent regions. Accurate prediction of transition onset is fundamental to the modelling of these flows. In most flow solvers based on the Reynolds-averaged Navier–Stokes equations, transition onset must be specified manually. To overcome this weakness and to more accurately predict aerodynamic flow fields, a boundary layer transition prediction methodology is presented. This methodology, which has been applied to a Navier–Stokes solver, dynamically locates transition onset as the flow solution is converging. The prediction methodology identifies several boundary layer transition mechanisms, including Tollmien–Schlichting instability, laminar separation and turbulence contamination. Where possible, the implementation utilizes the calculated boundary layer velocity profiles to strongly couple the predicted transition locations and the flow solution. The transition prediction methodology was used to predicted transition onset for the NLF(1)-0416 and S809 single-element wind turbine airfoils. Results obtained with numerical calculations are found to agree well with experimental observations. Copyright © 2001 John Wiley & Sons, Ltd.