Background: Small cell lung cancer is a rapidly progressive disease with high fatality. No sensitive and specific biomarker to assist in managing this disease exists currently. Aim: Role of pretreatment serum lactate dehydrogenase as a biomarker in small cell lung cancer. Methods: A hospital-based cancer registry was used to identify eligible patients from 1999 to 2009. Demographic data, lactate dehydrogenase level and clinical outcome of patients were collected for analysis. Results: One hundred and sixty-eight patients were identified: 61% (n = 103) males and 39% (n = 65) females. Majority had extensive stage (67%). High lactate dehydrogenase (≥230 U/L) was present in 60.4% (n = 75); mean reading 260 U/L (range 148–898 U/L) in limited stage and 470 U/L (range 116–5462 U/L) in extensive stage. Extensive stage patients with high lactate dehydrogenase had lower treatment response rate compared to those with normal lactate dehydrogenase (39% vs 79%, P = 0.002); no difference in treatment response was seen among patients with limited stage. High lactate dehydrogenase conferred a worse survival; mean overall survivals in limited and extensive stage were 8.0 and 5.2 months, respectively, in patients with elevated lactate dehydrogenase. Those with normal lactate dehydrogenase had an overall survival of 16.5 and 8.2 months, respectively. The association remained significant after adjustment for age, sex and treatment (HR 1.8, 95% CI 1.16–2.80, P = 0.009). Conclusion: High pretreatment lactate dehydrogenase is a prognostic marker of survival in both stages of small cell lung cancer. It is also a predictive marker of response to therapy in extensive stage. Larger prospective studies to validate our findings would be beneficial.