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To estimate the relationships of tobacco outlet density, cigarette sales without ID checks and local enforcement of underage tobacco laws with youth's life-time cigarette smoking, perceived availability of tobacco and perceived enforcement of underage tobacco laws and changes over time.The study involved: (a) three annual telephone surveys, (b) two annual purchase surveys in 2000 tobacco outlets and (c) interviews with key informants from local law enforcement agencies. Analyses were multi-level models (city, individual, time).A sample of 50 mid-sized non-contiguous cities in California, USA.A total of 1478 youths (aged 13–16 at wave 1, 52.2% male); 1061 participated in all waves.Measures at the individual level included life-time cigarette smoking, perceived availability and perceived enforcement. City-level measures included tobacco outlet density, cigarette sales without ID checks and compliance checks.Outlet density was associated positively with life-time smoking [OR = 1.12, P < 0.01]. An interaction between outlet density and wave (OR = 0.96, P < 0.05) suggested that higher density was associated more closely with life-time smoking at the earlier waves when respondents were younger. Greater density was associated positively with perceived availability (β = 0.02, P < 0.05) and negatively with perceived enforcement (β = −0.02, P < 0.01). Sales rate without checking IDs was related to greater perceived availability (β = 0.01, P < 0.01) and less perceived enforcement (β = −0.01, P < 0.01). Enforcement of underage tobacco laws was related positively to perceived enforcement (β = 0.06, P < 0.05).Higher tobacco outlet density may contribute to life-time smoking among youths. Density, sales without ID checks and enforcement levels may influence beliefs about access to cigarettes and enforcement of underage tobacco sales laws.