The port economics literature is extensive, but does not address well the economic effects of inland ports development. This paper explores the extent to which spatial proximity of inland ports vis-a-vis each other influences agglomeration externalities. Spatially lagged regression models are employed to analyse whether spatial dependence between proximate inland ports can be observed or, alternatively, whether the density of the inland port network in the Netherlands is leading to diseconomies of scale because of overproximity. The conclusions indicate that especially in the context of the dense fluvial network of the Netherlands inland ports development involves much competition among inland ports; being proximite to strong neighbouring inland ports is not necessarily beneficial to the growth prospects of an inland port. This indication of overproximity highlights a need for reflection on the possibility of an integrated and coordinated regional governance approach towards inland port development in the Netherlands and North-West Europe. The relationship between inland ports and regional development is obviously present, but ambiguous since it involves a multiplicity of interactions among a diversity of actors.