We examine the effect of the expansion of patient choice of health care provider on measures of process delivery and clinical outcomes central to the functioning of a health system, using a quasi-natural experiment in Spain over 2002–2019. We draw on a staggered adoption of provider choice reforms across Spanish regional health services and a heterogeneity-robust difference-in-differences estimator applied to regionyear panel data alongside individual-level survey data. We estimate that the availability of provider choice reduced specialist waiting times by approximately 17 days (19% of the pre-reform mean) and the use of private specialist visits, without increasing public health spending. The waiting-time and private-utilisation results are robust to excluding the region where the 2009 reform bundled choice with new hospitals, public–private partnerships, and a budget increase. Although we cannot reject zero effects on some clinical outcomes, the evidence is consistent with the thesis that provider choice improves the “quality needle”, namely it improves observable process quality without affecting less-visible clinical dimensions.