We investigate if Marine Stewardship Council (MSC) certified Norway lobster fishing vessels in Sweden got higher prices and sold larger quantities after certification was introduced in 2015. Using detailed daily panel data and exploiting the fact that the same fishing water contains both certified and non-certified vessels, we use a difference-in-difference model for analysing demand effects of MSC-certification. We find a price premium the first months after the launch of the certification scheme for the initial adopters. However, this price premium dissipates over time and is mainly found for trawler vessels. For trawlers, we also find a negative effect on sold quantities the first months after certification but a positive effect a few years after certification. Creelers, on the other hand, got a positive effect on quantities sold both immediately after certification and after a few years. No general effect of MSC certification is found on neither prices nor quantities when the entire period January 2012 – January 2018 is investigated.