These preexisting conditions include:
AIDS/HIV, lupus, alcohol abuse/drug abuse with recent treatment, severe mental disorders such as bipolar disorder or an eating disorder, Alzheimer's/dementia, multiple sclerosis, rheumatoid arthritis, fibromyalgia and other inflammatory joint disease, muscular dystrophy, cancer, severe obesity, cerebral palsy, organ transplant, congestive heart failure, paraplegia, coronary artery/heart disease, bypass surgery, paralysis, Crohn's disease/ulcerative colitis, Parkinson's disease, chronic obstructive pulmonary disease/emphysema, pending surgery or hospitalization, diabetes mellitus, pneumocystis pneumonia, epilepsy, pregnancy or expectant parent, hemophilia, sleep apnea, hepatitis C, stroke, kidney disease, renal failure, transsexualism.
Other conditions that could make it harder to purchase a health insurance plan, according to KFF:
Acne, allergies, anxiety, asthma, basal cell skin cancer (a type of skin cancer that doesn't tend to spread), depression, ear infections, fractures, high cholesterol, hypertension, incontinence, joint injuries, kidney stones, menstrual irregularities, migraine headaches, being overweight, restless leg syndrome, tonsillitis, urinary tract infections, varicose veins, and vertigo.