BACKGROUND/OBJECTIVE: SPIO is effective in sentinel node (SN) detection. No nuclear medicine department is needed, and no allergic reactions have occurred. This study aimed to compare retro-areolar and peri-tumoral SPIO injections regarding skin staining, detection rates and number of SNs. METHODS: Data on staining size, intensity and cosmetic outcome (0-5; 0 = no problem) were collected by telephone interviews with 258 women undergoing breast conservation. SN detection and the number of SNs were prospectively registered in 332 women. RESULTS: After retro-areolar and peri-tumoral injections, 67.3% and 37.8% (p