In the context of the emerging field of public health services and systems research, this study (i) tested a model of the relationships between public health organizational capacity (OC) for chronic disease prevention, its determinants (organizational supports for evaluation, partnership effectiveness) and one possible outcome of OC (involvement in core chronic disease prevention practices) and (ii) examined differences in the nature of these relationships among organizations operating in more and less facilitating external environments. OC was conceptualized as skills and resources/supports for chronic disease prevention programming. Data were from a census of 210 Canadian public health organizations with mandates for chronic disease prevention. The hypothesized relationships were tested using structural equation modeling. Overall, the results supported the model. Organizational supports for evaluation accounted for 33% of the variance in skills. Skills and resources/supports were directly and strongly related to involvement. Organizations operating within facilitating external contexts for chronic disease prevention had more effective partnerships, more resources/supports, stronger skills and greater involvement in core chronic disease prevention practices. Results also suggested that organizations functioning in less facilitating environments may not benefit as expected from partnerships. Empirical testing of this conceptual model helps develop a better understanding of public health OC.