The present research investigates how the number of issues affects the quality of outcomes in terms of joint gains and impasse rates in integrative negotiations. In the literature, two opposing positions exist reflecting a complexity dilemma regarding the number of negotiation issues: One position suggests that complex negotiations involving higher numbers of issues offer more trade-off opportunities, thereby providing negotiators with greater structural flexibility in reaching mutually beneficial agreements, which improves outcome quality. The opposite position emphasizes that the greater information load inherent in negotiating more issues impedes outcome quality. We propose a third, intermediate position: Negotiating more issues may only improve outcome quality up to a threshold, above which adding further issues results in deteriorated outcomes. We tested these propositions using a quasi-meta-analytic technique by examining the associations between the number of issues, joint gains, and impasse rates across multiple empirical studies on integrative negotiations using various negotiation tasks with different numbers of issues (N = 38,063/21,271 negotiations for joint gains/impasse rates). Moreover, we investigated whether factors related to how negotiators subjectively deal with the increased complexity associated with higher numbers of issues moderate the number-of-issues effect on joint gains. Multilevel analyses revealed no significant number-of-issues effect on joint gains up to a threshold of 3 issues but a negative effect for negotiations involving more than 3 issues. By contrast, we did not find a number-of-issues effect on impasse rates. Moreover, we did not obtain evidence for moderation effects. Findings are discussed with respect to their theoretical and practical implications.