The phase behavior of solvent-rich mixtures of glycerol monooleate and cetyltrimethylammonium bromide is reported for two solvents, water and aqueous solutions of 100 mM NaCl. The main concern is the properties of the lamellar phases and the formation of curvature defects within the bilayers. Defective lamellar phases are shown to form in both water and brine. The defective regions of lamellar phase are delineated by means of small-angle X-ray scattering (SAXS) studies. Direct visualization of the aggregate structure at high dilution is made by cryo-transmission electron microscopy (cryo-TEM). A rich micellar polymorphism is found, involving connected threadlike micelles as well as elongated micelles with noncircular cross sections. The correlation between the observed aggregate structures and the overall phase behavior is used to discuss possible defect geometries in the disrupted bilayers We also report that the water-based lamellar phase made from the intact bilayers seems to contain a large fraction of curved multilamellar aggregates. Interestingly, the corresponding bilayers that show curvature defects appear to build lamellar phases free of such textural defects.