Sacroiliac joint (SIJ) injection and arthrography have been described, yet no study has specifically categorized the morphological characteristics of SIJ arthrograms versus post arthrogram computerized tomography (CT). Forty-three patients with a mean age of 33 years (range 20-48 years) and an equal male to female distribution were studied radiographically for SIJ pathology. A total of 74 SIJ injections were performed using Image-intensifier-control and a posterior-inferior approach. Symptom reproduction indicating a provocation positive outcome, was reported in 63.5% with a mean injected volume of contrast media of 1.08 cc (S.D. 0.29). SIJ findings were then classified and scored in each aspect of the SIJ capsule by plain film arthrography followed by post arthrogram CT (anterior, posterior, superior and inferior aspects of the capsule). There was a significant direct correlation between the plain film and CT arthrography findings in each category (Kendall correlation coefficients 0.63 - 0.99, p<0.01). In addition, there was a significant direct correlation between provocation positive outcomes and volume of contrast injected (Kendall correlation 0.25, p<0.01; ANOVA, p<0.03). Post arthrogram CT revealed significantly more positive anterior capsule findings compared to plain film arthrography (McNemar's test, p<0.04). Conversely, plain film arthrography noted more diverticula compared to post arthrogram CT (McNemer's test, p<0.01). These findings demonstrate that a detailed radiographic analysis of the SIJ capsule is reasonable by either plain film arthrography or post arthrogram CT, with excellent agreement between the two techniques. Further, each test has specific regional benefits that may be appreciated in certain cases.