Treatment of metastatic breast cancer (MBC) has evolved during the last decades but it is largely unknown whether this has led to improved survival in the general MBC population. Based on the regional, population-based breast cancer registry, we identified 5,463 patients diagnosed with MBC in Stockholm County during 1979-2004. Patients were divided into five cohorts based on the year of first MBC diagnosis and observed and relative survival were compared across the cohorts after adjustment for potential confounders. A significant trend of better survival over time was demonstrated for patients 60 years or younger (P < 0.001, by log-rank test for trend), but not for older patients (P = 0.12) or for the whole MBC population (P = 0.13). The adjusted observed survival of patients ≤ 60 years was significantly improved in the 2000-2004 cohort (P < 0.001, hazard ratio = 0.7, 95% confidence interval = 0.58-0.84), corresponding to a clinically significant increase of median survival with more than 3 months and absolute increase of 5-year survival with 8% or more compared to previous periods. Similarly, relative survival analysis indicated a 31% decreased mortality for the younger subpopulation in the 2000-2004 cohort (P < 0.001). Systemic adjuvant treatment was a negative prognostic factor after distant recurrence. Treatment advancements in MBC are not reflected by better survival for the whole MBC population. An improvement is only observed after the year 2000 and is restricted to younger patients.