This paper presents first data on the udder health status of organic dairy farms in Northern Spain and analyses some management and productive characteristics related to milk production comparing with the conventional sector. Five certified organic farms from the Cantabrian Region were monitored monthly from February 2006 to January 2008 and individual samples of all lactating cows were taken from parturition to the end of lactation. Although organic farms in our study showed a great individual variability, overall these were small (<50 lactating cows) traditional farms, with a high degree of pasture (66-82% dry matter intake) and a milk production (average milk yield: 5950 L) 23% lower compared with the reference conventional sector (<50 cow farms). The organic farms had higher (p<0.05) average number of calves per cow (3.93) and a lower number of first-lactation cows (16.9%) than the comparable conventional farms (2.47 calves per cow and 33.1% first-lactation cows). Organic farms showed higher (p<0.05) somatic cell counts (SCC) than the reference conventional farms (mean log10±SD for all cows: 5.25±0.49 and 5.06±0.59, respectively). Detailed analysis of the SCC depending on the number of lactation and % of monthly SCC tests with linear scores indicative of udder infection suggest that while the heifers’ sanitary condition at the beginning of their productive cycle was similar in both types of farms, this seems to become worse along the productive cycle in the organics. This could be related to a low use of antibiotics for prophylaxis and treatment of udder infections and merits further investigation.