The various forms of Criorhina ranunculi (Panzer, 1804) in the canton of Geneva (Diptera: Syrphidae) with a key to separate the forms of this species. – The polymorphic species Criorhina ranunculi (Panzer, 1804) comprises visibly at least three different forms in Europe. Two of these forms are now known from Geneva, one of them closely resembling Criorhina pachymera. For the first time a key is presented, separating these two forms from one another and from C. pachymera. Records of C. ranunculi from Geneva are listed. It is concluded that the taxonomic status of the forms of C. ranunculi requires genetic investigation.