This paper studies the determinants of investment in legal advice by plaintiffs in patent litigation. A hand-collected sample of US patent litigation cases is used to identify the empirical factors that determine the number of legal counsels employed by the plaintiffs. It turns out that more valuable patents lead to a higher investment in legal advice. Large firms, and plaintiffs with large patent portfolios employ more counsels, whereas individual litigants employ fewer. Software patents are related to a lower investment by the plaintiffs. These findings help not only to understand the cost drivers of litigation but have also important implications for the discussions on software patents, and the role of the litigant status for litigation success.