What frequency does ISO 9001 require for measuring customer satisfaction?

Actually, ISO 9001:2008 doesn't require a frequency. All the ISO 9001 Standard stipulates is, "The organization shall monitor information relating to customer perception as to whether the organization has met customer requirements. The methods for obtaining and using this information shall be determined. (8.2.1)." This is an interesting case where aiming to meet the letter of the standard can get in the way of meeting the Standard because you are shooting for the wrong target. It's a bit like the question, "What is the minimum level of quality necessary to satisfy the customer?"

Enhanced customer satisfaction

My suggestion is, put the Standard aside. Decide, and I mean seriously decide, whether you are or want to be an organization that continually enhances customer satisfaction through the way you meet customer requirements. Assuming the answer is yes, what measures or criteria of success or failure in meeting this aim are you using, and are you monitoring them with sufficient frequency to give you sufficient information to know what to improve? ISO 9001 (8.2.1) offers a list of example tools: customer satisfaction surveys, customer data on delivered product quality, user opinion surveys, repeat/lost business analysis, compliments, warranty claims and dealer reports. (Ultimately, the most important criteria are:
1) Have you done business with them more than once and would you do business with them again?
2) Have you ever recommended them and would you recommend them to a friend?)

Don't do this in order to meet a standard. Do it to be a more successful company and you will not only meet the ISO 9001 Standard but you will also be a more successful company.

Voila!