Warren Buffett is very secretive about the actual holdings of public companies in the Berkshire Hathaway portfolio. In the Annual Report of Berkshire he only publishes what he has to under the SEC regulations. In a recent annual report he listed the following companies as his main holdings: American Express ($8.3b), Coca-Cola ($12.2b), Gillette ($3.0b) and Wells Fargo ($10.6b).
The value of the remaining equities (which he does not list) is around $10.5 billion.
However, the holdings of Berkshire are required to be reported to the SEC. Currently he has shares in 32 companies with 90% in the top 10 companies. So you could say that in practical terms Berkshire Hathaway has a portfolio consisting of 10 stocks. Apart from the four stocks listed above, the next six holdings in terms of size are Wesco Financial, Washington Post, Moody's, H&R Block, M&T Bank, and First Data
Apart from the holdings in Berkshire Hathaway, Warren Buffett personally buys a small parcel of 100 shares in companies that interest him and all of their competitors. He does this to make sure he gets all its annual and quarterly reports. These are kept in 100s of file drawers in the office of Berkshire Hathaway in Omaha, Nebraska.
He says that he skims a lot but reads "every single word from cover to cover" in the annual reports that interest him.
