Initiation and propagation of fatigue cracks in steel structures induced by repetitive actions are highly random due to both aleatory and epistemic uncertainties related to material properties, loads, damage, modelling and other factors. For this reason, a probabilistic approach is necessary to predict the fatigue crack growth damage. This study presents a probabilistic approach for combined inspection/monitoring planning for fatigue-sensitive structures considering uncertainties associated with fatigue crack initiation, propagation and damage detection. This combined inspection/monitoring planning is the solution of an optimisation formulation, where the objective is minimising the expected damage detection delay. Furthermore, this formulation is extended to a bicriterion optimisation considering the conflicting relation between expected damage detection delay and cost. A set of Pareto solutions is obtained by solving this bicriterion optimisation problem. From this set, a solution can be selected balancing in an optimum manner inspection and monitoring times, quality of inspections, monitoring duration, and number of inspections and monitorings. The proposed approach is applied to a naval ship and a bridge subjected to fatigue.