diff --git a/input/fsh/extensions/serviceEvent.fsh b/input/fsh/extensions/serviceEvent.fsh
new file mode 100644
index 0000000..df2ff86
--- /dev/null
+++ b/input/fsh/extensions/serviceEvent.fsh
@@ -0,0 +1,5 @@
+Extension: ServiceEvent
+Id: service-event
+Description: "Extension for service event id (*palvelutapahtuman tunniste*)."
+* value[x] 1..
+* value[x] only oid
\ No newline at end of file
diff --git a/input/pagecontent/StructureDefinition-fi-base-encounter-intro.md b/input/pagecontent/StructureDefinition-fi-base-encounter-intro.md
index 252c0a9..afd779e 100644
--- a/input/pagecontent/StructureDefinition-fi-base-encounter-intro.md
+++ b/input/pagecontent/StructureDefinition-fi-base-encounter-intro.md
@@ -41,20 +41,27 @@ and will archive lab results directly to Kanta. It receives encounter id in SMAR
 context. Laboratory system can resolve *palvelutapahtuma*'s OID identifier by fetching the
 encounter resource.
 
-##### How to communicate palvelutapahtuma via FHIR encounter?
+##### How to communicate the *palvelutapahtuma* via the Encounter resource
 
-First thing is to identify the appropriate aggregation level of encounter. If encounter is not
-representing a *palvelutapahtuma*, but is a lower level encounter (some systems call these
-*prosessitapahtuma*), `partOf` should be used to point to upper level encounter (up until
-*palvelutapahtuma* level is reached).
+This method is applicable for resources that have a direct link to Encounter.
 
-A *palvelutapahtuma* encounter is identified by an identifier. When encounter has an identifier
-with `use=official` it is considered to be a *palvelutapahtuma* and that identifier SHALL be the
-OID of a *palvelutapahtuma*.
+An Encounter that is a *palvelutapahtuma* SHALL have an identifier with `use=official` and the
+value of that identifier SHALL be the OID of a *palvelutapahtuma*.
 
 Other levels of encounter that are not a *palvelutapahtuma*, MUST NOT contain an identifier with
 `use=official`.
 
+The resource referring to the Encounter, may link to the *palvelutapahtuma* Encounter directly, or
+to a lower level Encounter (some systems call these
+*prosessitapahtuma*). In this case, the lower level Encounters SHALL have a chain of `.partOf`
+links eventually leading to the *palvelutapahtuma* Encounter.
+
+##### How to communicate the *palvelutapahtuma* without an Encounter resource
+
+When the resource does not have a direct link to Encounter or if the chaining of Encounter
+resources is considered too complex, the
+[ServiceEvent extension](StructureDefinition-service-event.html) can be used instead.
+
 #### Organizational responsibility
 
 The unit responsible for the encounter SHOULD be communicated using the `serviceProvider` property.
diff --git a/input/pagecontent/StructureDefinition-service-event-intro.md b/input/pagecontent/StructureDefinition-service-event-intro.md
new file mode 100644
index 0000000..e21b16b
--- /dev/null
+++ b/input/pagecontent/StructureDefinition-service-event-intro.md
@@ -0,0 +1,11 @@
+### Scope and Usage
+
+ServiceEvent extension defines related service event identifier (*palvelutapahtuman tunniste*).
+When the service event id is included into the resource, it SHALL be done with this extension. 
+
+The scope of *palvelutapahtuma* is described in the description pf the
+[Fi Base Encounter](StructureDefinition-fi-base-encounter.html#relation-to-finnish-palvelutapahtuma)
+profile.
+
+The Fi Base Encounter profile also describes how the *palvelutapahtuma* Encounter can be referred
+to using the link from the resource.