The thermotropic and lyotropic liquid crystalline phase behaviour of a series of diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains (geranoyl, H-farnesoyl, and phytanoyl) has been investigated. When neat, both H-farnesoyl and phytanoyl diethanolamide form a smectic liquid crystalline structure at sub-zero temperatures. In addition, all three diethanolamides exhibit a glass transition temperature at around −73 °C. Geranoyl diethanolamide forms a lamellar crystalline phase with a lattice parameter of 17.4 Å following long term storage accompanied by the loss of the glass transition. In the presence of water, H-farnesoyl and phytanoyl diethanolamide form lyotropic liquid crystalline phases, whilst geranoyl diethanolamide forms an L2 phase. H-farnesoyl diethanolamide forms a fluid lamellar phase (Lα) at room temperature and up to ∼ 40 °C. Phytanoyl diethanolamide displays a rich mesomorphism forming the inverse diamond (QIID) and gyroid (QIIG) bicontinuous cubic phases in addition to an Lα phase.