Suddenly HDFC mutual funds are underperforming and I am worried about my HDFC AMC stock.

It is true that a lot of the HDFC mutual funds are underperforming. However, they are just a part of a bigger universe of mutual funds. All HDFC AMC funds are not necessarily underperforming. So, one needs to evaluate and analyze the performance of the majority of funds before taking any decision.

Additionally, there are a lot of factors that make HDFC AMC a premium stock. It is important to probably work out a SWOT analysis and assess its business model thoroughly before making the decision to sell the stock. It's always better to make a well-thought-out decision while parting with a stock, else you may regret the choice later. This is especially true for investors who are looking at holding a stock for the long term.