The present review deals with studies performed during several consecutive years on the effect of air-curing on tobacco-specific nitrosamine (TSNA) formation and quality of tobacco. Temperature, relative humidity, water content and water activity data were collected during curing of dark tobacco in traditional air-curing barns and bulk-curing barns of different sizes, and chemical analysis of the cured tobacco were performed. The results from the screening study of the traditional curing conditions support the idea that a high continuous relative humidity during the entire curing period results in high TSNA levels in the tobacco, while a drier climate produces tobacco with lower amount of TSNA and nitrite. The study also demonstrates that a high continuous relative humidity at the beginning of the yellowing phase followed by a pronounced decline of relative humidity at the critical period for TSNA formation, i.e., when the plant cell membrane breaks down due to moisture loss and the cell contents become available to nitrite forming micro-organisms, results in tobacco with relatively low TSNA levels. Control of air-flow is important during the curing process and a uniform air-flow will increase the rate and amount of moisture loss from the tobacco, and also reduce possible gas-phase reactions between alkaloids and gaseous nitric oxides, derived from microbially generated nitrite, during air-curing of dark tobacco. Curing experiments, in mini- and bulk-barns with controlled conditions, aiming to mimic a reduction in humidity at the end of yellowing confirm that a decline in humidity at the critical period reduces the accumulation of TSNA in the cured tobacco, while still producing a satisfactory tobacco quality in a shorter time than traditional air-curing.