A new genus and species of primitive termite (Isoptera) is described and figured from the remains of an imago preserved in middle Eocene (Lutetian) Baltic amber. Idanotermes desioculus Engel, new genus and species (near to Mastotermitidae), is distinguished from related genera as well as all other termites known as inclusions in Baltic amber. In addition, the genus Heterotermes (Rhinotermitidae: Heterotermitinae) is newly recorded from Baltic amber and Heterotermes eocenicus Engel, new species, is described. A revised key to Baltic amber termites is provided so as to accommodate the newly discovered species.