Lovastatin, pravastatin, simvastatin, mevastatin, atorvastatin, fluvastatin and cervastatin and derivatives and analogs thereof are known as HMG-CoA reductase inhibitors and are used as antihypercholesterolemic agents. The majority of them are produced by fermentation using microorganisms of different species identified as species belonging to an Aspergillus, Monascus, Nocardia, Amycolatopsis, Mucor, or Penicillium genus, some are obtained by treating the fermentation products using the methods of chemical synthesis (simvastatin) or they are the products of total chemical synthesis (fluvastatin, atorvastatin and cervastatin). The present invention relates to a crystalline form of the sodium salt of pravastatin, which is known by the chemical name 1-naphthaleneheptanoic acid, 1,2,6,7,8,8a-hexahydro-.beta.,.delta.,6-trihydroxy-2-methyl-8-(2-me- thyl-1-oxobutoxy)-, mono sodium salt, which is useful as a pharmaceutical substance. The present invention further relates to the method for its preparation and isolation, to a pharmaceutical formulation containing the sodium salt of pravastatin in the crystalline form and a pharmaceutically acceptable carrier, and to a pharmaceutical method of treatment. The novel crystalline form of the sodium salt of pravastatin is useful in the treatment of hypercholesterolemia and hyperlipidemia.