The isolation of bis-amino-substituted carbenes of the Arduengo (3a) and Wanzlick type 4a has prompted us to look for stable nitrenium ions of the related structural type 3d(+) and 4d(+). Thus 5(+)I(-) (6(+)I(-)) and 18(+)ClO(4)(-) were isolated and structurally characterized by X-ray crystallography. Theoretical studies give insight into the different (electronic) structures and stabilities of 3a,d(+), 4a,d(+), and of related compounds.