diff --git a/README.adoc b/README.adoc
index 4fd415f45..88e194714 100644
--- a/README.adoc
+++ b/README.adoc
@@ -42,6 +42,9 @@ could set `logging.level.org.springframework.web.servlet.DispatcherServlet=DEBUG
 NOTE: Set `spring.application.name=bar` (for instance) to see the
 service name as well as the trace and span ids.
 
+IMPORTANT: If using Zipkin, configure the percentage of spans exported using `spring.sleuth.sampler.percentage`
+(default 0.1, i.e. 10%). *Otherwise you might think that Sleuth is not working cause it's omitting some spans.*
+
 :branch: master
 
 == Introduction
diff --git a/docs/src/main/asciidoc/README.adoc b/docs/src/main/asciidoc/README.adoc
index 71bebe740..f672bcb9c 100644
--- a/docs/src/main/asciidoc/README.adoc
+++ b/docs/src/main/asciidoc/README.adoc
@@ -40,6 +40,9 @@ could set `logging.level.org.springframework.web.servlet.DispatcherServlet=DEBUG
 NOTE: Set `spring.application.name=bar` (for instance) to see the
 service name as well as the trace and span ids.
 
+IMPORTANT: If using Zipkin, configure the percentage of spans exported using `spring.sleuth.sampler.percentage`
+(default 0.1, i.e. 10%). *Otherwise you might think that Sleuth is not working cause it's omitting some spans.*
+
 include::intro.adoc[]
 
 include::features.adoc[]