INDEX 600 STOCK FUND

Fund Overview

Adviser:

Mason Street Advisors, LLC

Objective/Focus:

The objective is to achieve investment results that approximate the performance of the S&P SmallCap 600® Index.

Asset Class:

Small-Cap Stocks

Style:

Blend

Investing in small company stocks involves a greater degree of risk than investing in medium or large company stocks.

Indices are unmanaged, cannot be invested in directly.

Fund Facts as of 12/31/17

Fund Inception

04-30-2007

First Available for Variable Annuity

04-30-2007

First Available for Variable Life

06-30-2011

Net Assets

$222.35 Million

Top 10 Portfolio Holdings % of Net Assets

iShares Core S&P Small-Cap ETF

2.1%

Nektar Therapeutics

1.1%

Chemed Corp.

0.5%

Healthcare Services Group, Inc.

0.5%

ALLETE, Inc.

0.4%

Cantel Medical Corp.

0.4%

Five Below, Inc.

0.4%

Spire, Inc.

0.4%

John Bean Technologies Corp.

0.4%

Evercore Partners, Inc.

0.4%

Total % of Net Assets

6.6%

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Disclosed Holdings

Sector Weightings % of Equities

Industrials

18.9%

Financials

16.0%

Consumer Discretionary

15.6%

Information Technology

13.7%

Health Care

13.1%

Before investing in a variable product, you should carefully consider the objectives, risks and charges associated with its investment options. For this and other information about a Contract, you should obtain the appropriate Contract and underlying fund prospectuses by contacting your Northwestern Mutual Financial Representative. Read the prospectuses carefully before you invest.

Mason Street Advisors, LLC (MSA) is the principal investment adviser for all the Portfolios in the Northwestern Mutual Series Fund (Series Fund). (Portfolios in the Series Fund are identified by the parenthetical next to the portfolio name.) MSA has engaged and oversees sub-advisers who provide day-to-day management for certain of the Series Fund Portfolios. Each sub-adviser may be replaced without the approval of shareholders. Please see the prospectus for more information. Additional fund options are advised by Russell Investments, Fidelity Investments, Neuberger Berman Investment Advisers LLC and Credit Suisse Asset Management, LLC

All securities are offered through Northwestern Mutual Investment Services LLC, (NMIS), Suite 600, 611 E. Wisconsin Avenue, Milwaukee, WI 53202, 1-866-664-7737. Member FINRA and SIPC. NMIS is a subsidiary of Northwestern Mutual.