For the first time, the temporal and spatial distribution of cloud-to-ground lightning over the western Mediterranean Sea have been studied. The monthly variation shows a single peak in September and October while minimum values are observed in January to March. The diurnal cycle shows a maximum on 0600--0700 LT and a minimum around 1600--1700 LT. The percentage of positive flashes is 8%, although it is higher in the winter than in the summer. The average multiplicity is 2.1 for the negative flashes and 1.1 for the positive flashes, and the percentage of single-stroke flashes is 48% and 91%, respectively. The annual distribution of multiplicity reveals a maximum in the summer and a minimum in the winter for the negative flashes. The median intensity was found to be 27.5 kA for the negative flashes. Positive flashes show maximum intensities in April and minima in August. The average maximum flash density is 1.5 flashes km-2 yr-1. The geographical distribution of density shows that the highest values are associated with the coastline and decrease eastward. The lightning activity over the island of Mallorca shows characteristics associated with both the land and the sea. The results are discussed in the context of the measurements taken for the land area of the Iberian Peninsula and for other oceanic areas.