1. The egg-laying behaviour in the wild of 51 butterflies in Sweden is studied: three different patterns emerge. Firstly, although the majority of butterflies deposit their eggs on the plants on which their larvae later feed, butterflies that overwinter in the egg stage and use herbaceous host plants tend to avoid laying their egges on host plants 2. Secondly, butterflies which use host plants that are superabundant, notably the grass-feeding satyrids, also tend not to deposit their eggs on the leaves on which the larvae later feed. Among the Swedish satyrids, two of the three species which do deposit their eggs on the larval hosts overwinter in the pupal stage, thus necessitating rapid larval development. 3. Thirdly, butterflies which use visually apparent host plants seem to find their host plants without having to alight on non-hosts, whereas butterflies that use hosts that are visually non-apparent frequently alight on non-host plants during the oviposition search before they find the appropriate plants. 4. The possible adaptive significance of these egg-laying patterns is discussed.