Exhibit 5.1

December 18, 2014

PDI, Inc.

Morris Corporate Center 1, Building A

300 Interpace Parkway

Parsippany, NJ 07054

Re:     Registration Statement on Form S-8

Ladies and Gentlemen:

Reference is made to the registration statement on Form S-8 (the “Registration Statement”) of PDI, Inc., a Delaware corporation (the “Company”), filed on the date hereof with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”). The Registration Statement covers (i) 1,250,000 shares (the “2004 Plan Shares”) of the Company’s common stock, par value $0.01 per share (the “Common Stock”), issuable by the Company pursuant to awards (“Awards”) granted under the Company’s Amended and Restated 2004 Stock Award and Incentive Plan, as amended (the “Equity Incentive Plan”), and (ii) 159,086 shares (the “Inducement Shares,” and together with the 2004 Plan Shares, the “Shares”) of the Common Stock, issuable by the Company pursuant to a non-plan based stock appreciation rights and restricted stock units awards to Graham G. Miao (collectively, the “Non-Plan Stock Awards”).

We have examined the Registration Statement, including the exhibits thereto, the Certificate of Incorporation, as amended from time to time, and the Amended and Restated By-laws of the Company, the Equity Incentive Plan, the Non-Plan Stock Awards, minutes of meetings and actions by written consent of the Company’s Board of Directors relating to the adoption, approval, authorization and/or ratification of the Equity Incentive Plan and the Non-Plan Stock Awards and such other documents as we have deemed appropriate in rendering this opinion. In our examination, we have assumed the genuineness of all signatures, the authenticity of all documents submitted to us as originals and the authenticity of all documents submitted to us as copies of originals. Based on the foregoing, we are of the opinion that (i) the 2004 Plan Shares, when issued and paid for in accordance with the terms of the Equity Incentive Plan and the applicable Non-Plan Stock Award, will be legally issued, fully paid and non-assessable; and (ii) the Inducement Shares, when issued and paid for in accordance with the terms of the Non-Plan Stock Awards, will be legally issued, fully paid and non-assessable.

We express no opinion herein as to the law of any state or jurisdiction other than the General Corporation Law of the State of Delaware, including statutory provisions and all applicable provisions of the Constitution of the State of Delaware and reported judicial decisions interpreting such laws of the State of Delaware and the federal laws of the United States of America.

We assume no obligation to supplement this opinion if any applicable law changes after the date hereof or if we become aware of any fact that might change the opinion expressed herein after the date hereof.

We hereby consent to the filing of this opinion as an exhibit to the Registration Statement. In giving such consent, we do not thereby admit that we come within the category of persons whose consent is required under Section 7 of the Act or the rules or regulations of the Commission thereunder.

Very truly yours,

/s/ Pepper Hamilton LLP

Pepper Hamilton LLP