Qualified medical expenses for HSA purposes are unreimbursed (not covered by insurance provider) medical expenses that could otherwise be deducted on Schedule A (Form 1040). For example, if you have a $1,000 hospital bill and your insurance covers $800 and you use your HSA to pay for the $200 that you owe, then the $200 is unreimbursed medical expenses paid for by your HSA.
The definition of what constitutes a qualified medical expense is very broad and includes expenses to diagnose, cure, mitigate, treat, or prevent disease. However, cosmetic surgery is not deductible unless it is related to disfigurement from a congenital abnormality, accidental injury, or a disfiguring disease. Other examples of nondeductible medical expenses are nonprescription drugs, doctor prescribed travel for "rest," and expenses for the improvement of your general health such as a weight loss program or health club fees (the weight loss program is deductible if it is to treat a specific disease).
Examples of deductible medical expenses include abortions, acupuncture, alcoholism treatment, ambulance costs, birth control pills, child birth classes, chiropractors, contact lenses, crutches, dentist, dentures, doctor fees, drug addiction treatment, prescription drugs, dyslexia reading programs and tutors, eye examination and glasses, guide dogs, health insurance, hearing aids, hospital bills, insulin, laboratory fees, long-term care insurance, nursing home if for medical treatment, optometrist, osteopath, physical therapy, psychiatrist, psychologist, travel to medical clinics, vasectomy, and wheelchair. This list does not contain every medical deduction available.