Aetna 10-Q 2015 Q3 Quarterly report

Exhibit 15.1

Aetna Inc.

Hartford, Connecticut

Re: Registration Statement Nos. 333-52120, 52122, 52124, 73052, 87722, 87726, 124619, 124620, 136176, 136177, 168497, 168498, 176009, 176011, 188792, 188814, 190272, 197707, 200647 and 206289

With respect to the subject registration statements, we acknowledge our awareness of the use therein of our report dated October 29, 2015 related to our review of interim financial information.

Pursuant to Rule 436 under the Securities Act of 1933 (the Act), such report is not considered part of a registration statement prepared or certified by an independent registered public accounting firm, or a report prepared or certified by an independent registered public accounting firm within the meaning of Sections 7 and 11 of the Act.

/s/ KPMG LLP

Hartford, Connecticut

October 29, 2015