The objective of this review is to describe characteristic MR mammographic findings for signal increase and morphological patterns of enhancement in pure ductal carcinoma in situ (DCIS) and to differentiate between high grade and non-high grade lesions. The dynamic MR examination (1.5 T unit, contrast enhanced T(1) weighted two dimensional fast field echo, 96 ms repetition time, 5.0 ms echo time, 80 degrees flip angle) of 39 consecutive patients with pure DCIS was evaluated retrospectively. Categories were defined for signal increase (C1=normal, C2=slow, continuous, C3=strong initial and slow further increase, C4=strong initial increase followed by a plateau phenomenon, and C5=strong initial increase followed by a washout phenomenon) and morphological patterns (M0=no pattern observed, M1=linear or linear-branched, M2=segmental dotted or granular, M3=segmental homogeneous, and M4=focal spot-like). Time-intensity curves showing a C4 and C5 signal increase were considered suspicious for malignancy. All cases were correlated with histology. 62% of all tumours had a plateau or washout (C4, C5), 77% showed a strong initial signal increase (C3-C5). On evaluation of time-intensity curves alone MR mammography (MRM) findings were suspicious for malignancy in 62% of all DCIS cases. A segmental enhancement was found in 82% of all enhancing tumors and the M2 pattern in 73%. In a combined analysis of signal increase and morphology, 70% of non-high grade and 92% of high grade DCISs were correctly described as suspicious. The difference between non-high grade and high grade DCIS was not significant (p=0.148), while significant differences were found between G1 and G3 DCISs and between G1 and G2 DCISs (p<0.05). All G2 and G3 DCISs showed noticeable signal enhancement. The mean histological tumour size of non-high grade DCISs was smaller than that for high grade DCIS (p<0.05). The hallmark of DCIS on dynamic MRM was unilateral segmental enhancement, most commonly with a granular dotted morphology (M2). Hormone effects need to be considered as the main differential diagnosis. Signal enhancement kinetics similar to invasive carcinoma were seen in the majority of cases. A combined analysis of morphological pattern and signal enhancement considerably improved rate of detection. G2 and G3 DCISs were correctly diagnosed with a significantly higher rate of detection (92%) than G1 DCIS (53%) (p<0.05). Different average size of G1, G2 and G3 DCIS on pathology cannot be excluded as a reason for differences found. Normal MRM seems to exclude high grade DCIS.