We study the effect of a 2006 reform to Italian family law that made joint custody the default for separating couples. The reform boosted joint legal custody by about 75 percentage points. Our research design uses difference‐in‐differences to estimate reform effects on the likelihood of a contested settlement, length of trial, and transfers between separating parents. The analysis is based on Italian individual‐level administrative data, which cover the entire population. The joint custody default appears to have increased dispute rates and length of trial markedly, without affecting transfers. There is no evidence that mothers buy custody rights back through reduced support. Our findings are consistent with the excessive discretion given to judges on some aspects of law implementation, which resulted in a partial application of the reform.