We have investigated the solubility, thermal stability and structural transitions of DNA complexed with the cationic surfactant dodecyltrimethylammonium bromide (DTAB). The study was done over a broad range of ethanol/water mixtures. The dependence of solubility on surfactant and salt concentration was studied. For low salt concentrations, it was found that DNA-DTA complexes are soluble at an ethanol content higher then 57% v/v; however, addition of excess DTAB increases the ethanol concentration at which the complexes begin to solubilise. At higher ethanol concentrations (about 80% v/v) DNA-DTA complexes were soluble over the entire range of DTAB concentrations investigated. Also at higher ethanol concentrations it was found that the DNA underwent a helix-coil transition. Circular dichroism data indicated that excess surfactant inhibited the B-to-A transition. In the presence of 5 mM NaBr, the DNA was found to be insoluble in the high-ethanol region, while the surfactant-dependent solubility line was shifted to lower ethanol concentrations. We present the phase diagram describing the solubility and conformational state of the DNA-DTA complex and discuss the influence salt has on its stability and solubility.