We attempted to determine how formal management control systems (MCS) are used by project managers in IS development (ISD) contexts. This involved investigating the antecedents of two types of project MCS use (interactive and diagnostic), and their direct and moderated impact on project performance. PLS analysis of data collected in a survey of 93 projects indicated that project managers’ level of discretion positively affected their level of interactive use of project MCS but did not influence their diagnostic use. Our findings also showed that interactive use of MCS enhanced performance when task uncertainty (task novelty and complexity) of an ISD was high, but worsened it when task uncertainty was low. Finally, diagnostic use of MCS apparently increased project performance when an ISD task uncertainty was low, but did not reduce it when task uncertainty was high. Overall, these results were stable across different size projects