Cross-cultural studies have found national differences in how concerned people are about online privacy. However, it has not yet been settled what causes this variation, and several factors have been proposed in the literature, including internet habituation, individualism, and uncertainty avoidance. Here we investigate these factors by two studies. In the first, we examine the association between online privacy concerns and a new measure of online self-disclosure norms that we introduce. We find that this measure is significantly associated with two established instruments of online privacy concerns in the literature. In the second, we analyze previously unpublished data from a questionnaire on online self-disclosure norms as assessed by this new measure. It includes replies from 18,046 adult respondents from 57 countries and six continents. We find that norms in favor of more restrictive online self-disclosure are weaker in countries with higher levels of internet penetration (r = −0.56, p < .001). Our findings suggest that higher internet penetration in a country reduces online privacy concerns. The results support the idea that habituation to online environments decreases privacy risk perceptions. An implication is that preferences for online privacy are likely to decline over time in countries where internet penetration is still low. Lastly, in conflict with previous studies, our analyses do not support the theory that online privacy concerns are associated with national cultures related to individualism or uncertainty avoidance as measured by Hofstede's indices.