According to the Los Angeles County Department Coroner's office, troubled baby-oil heiress Casey Johnson died of diabetic ketoacidosis -- meaning she didn't have enough insulin in her body.

Read the Coroner's report HERE

The autopsy  was performed on Johnson January 5th, but the LA coroner's office  had to wait for toxicology results before making an official ruling.

Johnson's body was discovered at her Los Angeles home on January 4th, it is believed she had been dead for several days when her corpse was discovered.

Johnson had struggled with diabetes since childhood and was supposed to give herself regular insulin injections.

She didn't, according to  gal pal Tila Tequila.