This paper examines the extent to which sectoral diversification can act as an insurance mechanism against fluctuations in regional gross value‐added growth rates. Portfolio theory is applied to the growth‐instability properties of German districts. Furthermore, a comprehensive diversification measure is defined. Stochastic Frontier Analysis is deployed in order to estimate whether diversification allows regions to achieve more efficient growth‐instability combinations. The results confirm that diversification does generate such effects. Spatial interactions do also play a role: The effects are less pronounced for regions whose economic performance is mainly driven by the surrounding regions.