Effects of environmental enrichment on activity, behaviour, walking ability, contact dermatitis and performance were investigated in fast- and slower-growing broiler chickens. A total of 840 day-old male broilers, 420 of a fast-growing strain (Ross 308) and 420 of a slower-growing strain (Hubbard JA757), were housed in a 2 × 2 factorial arrangement, using a complete randomized design. Broilers were housed in 28 pens of 3 m2 in one climate-controlled room. Half of the pens per strain were enriched (EE) with barrier perches, ramps, platforms and a dustbathing area, and the other half of the pens were not enriched (NE). In the EE pens, also black soldier fly larvae were provided daily in the dustbathing area and broilers in NE pens received an additional protein-fat mix, to achieve similar energy and nutrient intake compared to the EE treatment. Behaviour was observed by scan sampling and focal sampling in weeks 2, 4, 5 and 7. Walking ability, footpad dermatitis and hock burn were measured in three broilers per pen at a body weight of 1.7 and 2.6 kg. Performance was determined weekly. Results showed that in the enriched environment, at the same age slower-growing broilers made more use of provided enrichment materials than fast-growing broilers (P < 0.001; Δ = +13.5 %). Providing enrichment decreased the proportion of slower-growing chickens standing idle, whereas this effect was not found for fast-growing broiler chickens (P = 0.006; Δ = -2.8 % for slower-growing broilers). Furthermore, at the same age, more slower-growing broilers were active (Δ = +4.5 %) compared to fast-growing broilers, whereas fast-growing broilers showed more sitting idle (Δ = +4.2 %) and ingestion behaviour (Δ = +2.8 %) than slower-growing broilers in both EE and NE pens (P < 0.05). Broilers of both strains in EE pens showed longer duration of activity (P < 0.05; Δ = +11.3 %) compared to broilers in NE pens. No effects of enrichment or strain were observed for walking ability and contact dermatitis. Fast-growing broilers and broilers in NE pens had a higher average body weight, a higher average daily gain and a higher feed intake than slower-growing broilers and broilers in EE pens, respectively. In conclusion, environmental enrichment was most used by slower-growing broilers and providing enrichments increased activity to a similar extent in both strains. However, providing enrichments did not improve walking ability and had an adverse effect on performance in both strains.