First, your letter goes to the department considering your admission, not the admissions office. 🙂

The purpose of the statement of purpose / letter of intent is to convince the graduate admissions committee of each department to which you are applying that you are an excellent candidate for admission to THAT particular department.

Here’s what you should include:

(And it does not matter in what order. Just make sure your narrative makes sense.)

Your academic interests, and how your academic background suits you for further study of these interests. Be as specific as you possibly can, making SURE to show your familiarity with current theory and method in your intended area of study!

Delineate your goals, too. (Do you intend to become a professor? a researcher? Do you want to work for an NGO or a nonprofit? Say so.)

If there are blemishes on your record, explain them. For example, if you were working 30 hours a week as an undergrad, this might help the committee understand a less-than-perfect GPA.

Be sure to include any information about you that cannot be found on your undergraduate transcripts (like awards, special projects you did, independent studies, work experience related to your field of study, etc.)

Articulate your reasons for choosing THIS particular program. Show familiarity with the faculty and their fields of specialization. Don’t just list the faculty – specify with whom you’d like to work and why.

Mention your desire to be considered for teaching assistantships, research assistantships, or fellowships. But only briefly. Like once.

You didn’t ask about the writing sample, but I’ll throw in some advice about that for free. 🙂

The expectation in regard to your writing sample is that it will be an academic paper that you’ve written recently. Ideally, it will illustrate your ability to do solid research in your area of interest, employing your preferred methodology. Be sure to follow exactly the length requirements, as this differs at every program.

And for goodness sake, proofread everything. Statements or writing samples with spelling or grammatical errors go directly to the bottom of the pile, so to speak.

Best wishes to you!

Ya know, I’m going to say considering the nature of the degree it would be acceptable. Now as others have said it may not be standard practice so don’t make it the focal point of the paper, but if you have 5 pages to fill and designate just short few sentences at the end of the essay to make this point, I don’t think it will make/break you…I’ve heard of people going to law school/writing admission letters because of tragedies in their lives (Nancy Grace’s former lover murdered) and people going into physical therapy because they were injured as an athlete and had dealings with those professionals who influenced them (an example is eluding me here but there was one locally at least)…. Anyway — its largely a judgment call…I’ve been to grad school and can’t remember at all what I wrote about, but I’m sure some of it was “personal” in nature. Good luck.