Do I need to report a foreign brokerage or demat account under FATCA if it holds no cash?

Yes. FATCA's Form 8938 covers specified foreign financial assets, which include foreign brokerage and demat accounts even when they hold only securities rather than cash. The FBAR similarly treats a foreign securities account as reportable. The value you report is the account's total worth, including the market value of the shares inside it, not just any idle cash balance. A common mistake among newcomers is assuming a stock-only account is exempt because it has no rupee or euro cash. It is not. Also note that foreign mutual funds held in that account may separately be PFICs requiring Form 8621. Report the account on the FBAR and, if you cross the FATCA threshold, on Form 8938, and evaluate PFIC exposure on any pooled funds inside.