Short-term rents of rooms or apartments in the most important tourist cities have significantly increased in the last decade, also thanks to spread of dedicated smartphone apps and web platforms. These types of accommodation now constitute a significant part of the tourist accommodation facilities, however this under-regulated development has introduced some advantages but also some drawbacks, making it necessary to get an exact measure of this phenomenon. Official statistics are quite lacking in this sector, so we used, as alternative sources of information, two of the main short-term rentals brokerage platforms (AirBnB and Booking) to estimate the extent of the phenomenon in Florence.