This paper analyzes the effect of banking relationships on interest rates and the probability that guarantees must be provided in a sample of small and medium-sized enterprises (SMEs). The results indicate that SMEs that work with fewer banks obtain debt at a lower cost. This seems to suggest that concentrated banking relationships reduce the uncertainty of lending to risky firms, which translates into lower interest rates. Reduction in risk could come from greater flexibility in negotiations, increased control over the investment, and mitigation of the free-rider problem. When the relationship is exclusive, which would represent the maximum concentration, a bank can take advantage of its monopoly position and require more guarantees from a firm. SMEs that have longer-term relationships with their bank are more likely to be required to provide guarantees. This result seems to suggest that SMEs involved in longer-term relationships are subject to the information monopoly of the lender.