How the SNS works (and where the cracks are)
The Sistema Nacional de Salud is decentralised. The central Ministerio de Sanidad sets the broad rules; each of Spain's 17 autonomous communities runs its own public health service (SAS in Andalucía, SERMAS in Madrid, CatSalut in Cataluña, Servei de Salut in Valencia, etc.). The funding is tax-based, and once you're inside the system there is no per-visit charge for GP visits, specialist referrals, hospital care or planned surgery.
The crack: capacity is tight. Andalucía and Madrid are functioning well; Cataluña has been openly struggling under load since 2023; the islands (Mallorca, Canarias) have specialist-shortage backlogs. Family doctor (médico de familia) allocations in growth areas — Alicante province, Málaga capital, parts of Valencia city — can take 4-8 weeks from registration. Once allocated, weekday appointment availability is usually 24-72 hours. Specialist referrals can be 6-16 weeks depending on the speciality and region.
The day-to-day card is the Tarjeta Sanitaria Individual (TSI), issued by your regional health service after you register at a Centro de Salud with your padrón certificate and proof of system entitlement. Carry it to every appointment; everything is keyed to its number.

