Yes. Here is what the IRS says in their 2012 Medical and Dental Expenses Publication 502:

Guide Dog or Other Service Animal—
You can include in medical expenses the costs of buying, training, and maintaining a guide dog or other service animal to assist a visually impaired or hearing-impaired person, or a person with other physical disabilities. This includes any costs, such as food, grooming, and veterinary care, incurred in maintaining the health and vitality of the service animal so that it may perform its duties.

The federal tax law defines medical care as "diagnosis, cure, mitigation, treatment, or prevention of disease, or for the purpose of affecting any structure or function of the body." That sounds like it can include costs related to a service animal that mitigates a medical condition.

In Publication 502, the IRS states:

"Guide Dog or Other Service Animal - You can include in medical expenses the costs of buying, training, and maintaining a guide dog or other service animal to assist a visually impaired or hearing disabled person, or a person with other physical disabilities. In general, this includes any costs, such as food, grooming, and veterinary care, incurred in maintaining the health and vitality of the service animal so that it may perform its duties." www.irs.gov/publications/p502/ar02.html#en_US_2012_publink1000178936

Medical expenses are an itemized deduction and only deductible if the total, less any reimbursements, exceeds 7.5% of your adjusted gross income for the year (10% starting in 2013 except for "seniors" who get to use 7.5% through 2016).

I agree with the others except, if the service animal assists the person in being able to make taxable income the expenses can be taken on a 2106 and only subject to2% reduction as opposed to a 7.5% reduction of the AGI.