This article examines recent growth and diversification strategies of mountain farms in the northwest of Spain and the challenges that lie ahead. The data were obtained from a survey of production and household characteristics, assessing the effect on strategies of the location and the characteristics of the farm and farmer. The small size of farms has influenced farmers' strategies for growth and diversification. Extensification has been pursued by a minority of farms because of their inability to reach viability with limited size. Diversification is low in agriculture and in other activities linked to the farm, as it is driven by the constraints imposed by resources and age. Consequently, pluriactivity is the more common form of farm diversification despite the limitations of the local economy. Agriculture is in danger of deteriorating further in the medium term, as one third of farms are marginal and in transition to disappearance, and another half of farms are in a fragile situation due to their low income levels. The disappearance of 4 out of 5 farms and a third of agricultural land in the period 1982–2009 has drastically reduced traditional livestock activity.